Nimble quick to send letters of handover with NO INFORMATION! I DONT HAVE ANY OUTSTANDING ACCOUNTS WITH CELL C!

This is another complaint about Nimble (although its not regarding the same account as before) I received another letter from Nimble to say now I owe someone else (Cell C) The same thing happened with Home Choice and I long timed paid them. Now they are saying I owe CELL C. I do not have record of any other CELL C Account as I just recently cancelled my only cell c account I had. The contract was expired so there was only 1 month notice. I dont have emails or calls from CELL C for anything else and I am 150% sure I dont have more accounts with them. The problem is when you try to contact Nimble they don't answer. The statement they send to me I cannot open using the password they supply. They are not sending me any info from Cell C, Just that i owe them with a nimble letter. It is horrible to have these people on your backs but they not able to be reached! With my Homechoice account I had to log a dispute with credit bureau as I long time paid, that has been resolved now after many months, and here we go again??????