Nagging Debt Collectors

My two accounts with Standard Bank were handed over to this firm. I settled both accounts at the.beginning of April 2020 and I unfortunately swapped the two settlement payments around. I received a phone call to write to them that I had swapped the.payments around, I did. Then I received a call that I.must send.them proof of settlement if the accounts and I did. I am however still being phoned by different consultants inquiring about when I am making my next payment or when am I settling. I have fights with them each time because for some reason their system does not update the way its should it should as each consultant has a reason why they are phoning me about accounts I have settled. Can they jerk-up their systems instead of becoming an annoyance to clients who have settled their accounts.