breach of contract

I took a fixed monthly contract cell phone with Telkom around May 2016 by telephone(no contract was signed), in August 2016 they debited more than what we agreed on and they send a statement. I contacted them by phone with the dispute and they promised to fix the problem, I reversed the transaction. the following month they did the same thing and this time the sim card was already blocked, again they promised to fix the problem which they never did until I stopped calling them and I kept reversing the transactions from them monthly because the sim card was blocked in any case. they send me a mail (Good Day, MGOBOZI VUYISWA Our Reference Number: ND ********** 0

We have been instructed by our Client Telkom Mobile to collect your outstanding debt to the amount of R 2,138.93 for services rendered.

Be advised that you current landline number under this contract will not be ported or be made available to you if the amount outstanding is not settled. Our client reserves the right to release your number to the network to be linked to a different consumer). I explained to them what happened and they request proof which I don't have. I then advised them to get the telephone recordings from Telkom because everything was telephonically from the beginning, now they threatening me with sms 's ( Final Demand: Mgobozi despite numerous demands your Telkom Mobile acc ********** 95 remains in default of R2138.93, we have instructions to issue summons . Tel ********** 668)