Keep Receiving Debt Collector Calls

I had a delinquent account due to not knowing a student loan was not being paid, since mine are on autopay except this one which gets sent to my family's house. Anyways, the school sent it to collection; however, I spoke with my school within a day or two of it occurring and paid the full balance remaining. This was a month and half ago; the account was paid in full and have no more payments in that loan. However, collections keeps calling. I have not answered them, because I owe nothing; but the calls are everyday including weekends. Before I answer them to stop it, what info should I prepare myself with? The account was sent to collections; however, the school reversed it a day later since my payment went through for the whole balance. I have records, payment dates and everything with the school. Thanks for all the help.