rude collections company

We settle our game account in march 07/03/2018 and we sent the proof of payment to email address that was provided to us, today my husband got a call from a collections company about an unpaid game account, we paid off this account why are we getting these calls from rude and disrespectful people.

We have no contract with the collections companies and we do not have to get any calls from them more especially because we paid off that account, we need feedback by end of business with an apology letter and confirmation that you guys got all your money .