Using Pagination Library

You have only two ways to solve your problem.
1. Use pagination of the model.
2. Write your own implementation of pagination.

I recommend the second way. Only then will you understand how pagination works.
And then, looking at the original code, you will feel ashamed.

A comment about your code.
$db->query() returns the query result.
Services::pager() returns an instance of the pagination class.
But they are not related to each other.
What kind of magic do you expect?