Settlement letter NOT received

I settled my Absa cheque account with MacRobert Attorney, dealing with Karabo Madingoana and she said they will send me paid up letter within 3 days. It's been 5 weeks and I am still waiting for the letter - NS070761. I sent the POP numerous times but they claim they did not receive the proof of payment!!! I need the settlement letter as there is another company Imbuyiso Collections trying to make me pay a settlement for the same absa cheque account - they do not want to believe the account has been settled!! I need to send the letter to them!