Given up to debt collectors after settling my accounts

I never complain but Cell C just put me in a situation where I have to, due to lifestyle changes I decided to stop all my cellphone contracts(4 with cell C) and payed allmost 10 000 rand in settlement fees. This was in march 2021, this morning a independent debt collection company phones me and tells me tgat i have been handed over by cell c for owing them an amount in access of 7500 rand, this after I had received confermation messages from cell c that all my contracts had been settled, this is not even the worst, in april 2020 I took my galaxy s9 in for repairs, then lockdown happened and i was without a phone for a long time! And when i tried finding out where the phone was or what the hold up was the repair centre said that they knew nothing of my phone, this persisted for more tgan 8 months untill my contract expired and i upgraded to a new device, then I gad to go to cell c lichtenburg myself and go get the phone from the manager who promised me that it was sent in for repairs but had been returned to to paperwork issues, i took the phone to cell c rustenburg then but was told that the phone is no longer insured as i have upgraded, this made me cancel all my contracts with them and cost me a hell of a lpt of money just to be told today that i owe them more than 7500 rand, it is pathetic, never have I before complained openly but Cell C has to be made public for this as I can be certqin that I am not the first, nor will I be the last person that this will happen to