Complaint about amondo Telkom

I have had the worst experience ever with mondo (telkom) I was paying R139 for 11GB of data and a pocket router, they called me 2months before the contract would end and they asked if I would like to continue with the contract and I said because telkom network is unstable where I stay, then the contract my 25 months was done then,they started deducting R40 from my account then R80 then R120 until I noticed that this money is doubling now they take R1400 sometimes they take R800 I now have a job of reversing the payment and the bank is charging for that I don't know what the money is for and why are they still deducting so much when I go to telkom offices they say I have a contract with mondo and not them