I don't think this is a project management question - you haven't described anything in the context of a project - the situation seems more line/operations management. That said, Mr. Espina has persuaded me to think about the problem in the terms of project management.
Communications is a project management skill. From my perspective and based only on the information you've provided, you have a communications problem and you're making it worse.
He was unsatisfied with solution and I asked him, many times, to meet me for further clarifications. He is misbehaving and writing mails instead of meeting and solving all the issues.
Terms like "misbehaving" are judgmental, and they communicate a very clear message to the employee. They communicate that the employee's options are to behave or to misbehave, and that you are the arbiter of proper behavior. This concerns me greatly from a corporate HR official. If my HR head expressed this much contempt for me, I would feel compelled to begin to defend my position. I would shift all communication from oral to written and contact legal counsel.
In the context of "misbehaving and writing emails", you've communicated a contempt for those of us who prefer email communication. Many of us in technical professions live and breathe by emails. Many of us have been subject to the tyranny of meetings that prolong discussions and never resolve issues. (The actually issue and resolution isn't clear from your posting, presumably out of respect for the employee's privacy). Many of us in the technical profession prefer record copies of communication - particularly communications that can affect our pay or benefits.
If you are trying to discuss the matter in meetings (a non-record medium) and the employee is trying to discuss the matter in emails (a record medium), then the conflict may have already escalated beyond the point where you can exert control.
[Aside: It is possible that I have misunderstood the situation - if the employee is writing emails about you and your company to others outside HR/Line management, then the problem is quite different. ]
It isn't clear to me what the desired outcome/action is, but in general, if I want an action (and in this case you want to close this issue with the employee), strategy compels me to choose a communications style that is acceptable to the individual who must take the action. When I communicate with my boss or my senior stakeholders, I choose the communications method they prefer. I don't demand meetings if they prefer phone calls. In this case, you're frustrated that he prefers a different communications style, but your requests that he follow your preferences haven't been productive; trying the same thing again is going to both be unproductive and communicate even more effectively to the employee. Continuing down this path is a clear communication that you do not respect the employee.
You're asking for a sample memo, but I don't know what the sample memo is intended to convey. Is it a written warning? a memorandum for the record? What is it you want to communicate to the employee? What is the message?
I recommend that you take a step back and determine what you want from this employee. What is the outcome you want?
I'd ask the employee outright what outcome the employee wants - this conflict has escalated - what would de-escalate it and keep the employee satisfied.
Is settling the issue worth responding to his emails? Does your organization have a process for escalating employee disputes? do you have an alternative resolution procedure? If not, I would invite the employee to work with me to establish that procedure and document in Organizational Process Assets. I'd ask the employee to help me craft a memo that could be used the next time an employee and HR cannot agree on the resolution.
Let me return to project management in closing. PM's care about closing the project. Everything we do is in the context of "What impact will this have on the project?" Your communications & interactions with this employee have decreased the value of the employee to the project and to the company. Until this issue is resolved that employee is unhappy and that unhappiness impairs productivity. This issue is costing the company money, productivity and progress. I urge you to reconsider the issue not as "employee being disrespectful", but as "An issue which is damaging employee productivity and needs to be resolved to mutual benefit."
(PostScript - I mentioned this above, but I acknowledge that I may have completely misunderstood the problem; you are (properly and correctly) concealing the issue from us - that is your professional obligation. If I've inferred material which is inaccurate, then I apologize; you asked for advice and I've given the best advice I could within the constraints of the information you've provided and the methodology of project management. I don't pretend to be an HR professional.)