Cell C account in arrears without any notification and slow assistance

I had a number of cell phone contracts with Cell C and reduced them over time. At the end of November my last 3 contracts finished and I stopped them. I decided to take out a new contract on the one number and then supp**** the necessary documentation only to receive an sms without any follow up from Cell C that my application was denied. When I followed up after great difficulty through their call centre they indicated that I owed and amount of just more then R600 since 2017. I went back to all my e-statements and forwarded to them showing that my accounts were never in arrears and even the number in question up to the last month of the contract was in the clear. I am still waiting for them to respond. Very slow and poor service and I think extremely bad that according to them there is an outstanding amount yet I had no such communication from them and my Cell C statments are all ineth clear.