Unfair treatment by Cell C

I took out Cell C contract u till sometime last year I had financial difficulties, in Jan 2020 I made contact with their legal department to make arrangement to sort out and fix my account with them as well as to reinstate my service. I was advised to pay R1000 at the end of Jan 2020 but before end of that month I got call from someone(think external party?) telling me that I have to pay R5800 for my cell c account. My frustration come where I am not sure why am I been treated like that, I know I didn't conduct my account well. But that been the case cell c agreed that I pay R1000 and they would then reinstate my service and I continue pay my contract for an amount of +/-R300. The other problem is when I saw I was drawing I called Cell C to cancel one of the numbers that the contract was ending end of Jan 2020 but they refused citing that I was In areas so that I feel was not treating me right because we could have avoided this situation before it got worse.