Q. Will I get something in the mail saying how much interest I was reimbursed?
A. You'll have to ask the loan Co that question?
I'm surprised you didn't get paperwork when you got the money. You MAY get a 1099-C in January or February. If so, it will be broken down between interest an principal.
You say you were "reimbursed for all the payments". That would indicate that you use the amount your deducted on past tax returns to declare income for the current year.
Forgiveness of student loans is usually not taxable, even if you got a 1099-C. Reference: https://www.investopedia.com/form-1099-c-understanding-your-1099-c-form-4782275
