Updating user profile matrix block with plugin (Craft 3)

Question

I am working on a plugin for Craft 3 that will add new matrix data to users profile and keep the old/current data that is in the matrix field.

I have been looking at these but they are for Craft 2 so maybe that's the problem:

• Updating user profile matrix block with plugin

• Creating a matrix entry with a plugin

The below is what I have tried but getting the error "Class 'controllers\MatrixBlockModel' not found"

$member_id = Craft::$app->getUser()->getId();
$dateCreated = date('Y-m-d H:i:s');

$block = new MatrixBlockModel();
$block->fieldId = 77;
$block->ownerId = $member_id; //Users ID
$block->typeId = 11; //Block Types ID
$block->ownerLocale = 'en_us';
$block->sortOrder = 1;

$block->getContent()->setAttributes(array(
    'fileDownloaded' => 'fileDownloadedxxxxprotectedlinks_links',
    'manufacturer' => 'manufacturerxxxxprotectedlinks_links',
    'date' =>  $dateCreated,
));

$success = Craft::$app->matrix->saveBlock($block);

I also added:

use craft\elements\MatrixBlock;

Any ideas?