Device obligation carry over

I have a contract with telkom, they called me and informed me it was due for an upgrade @23 months, i upgraded nd got a new deal. Nd now they sent me a statement of R1135 while my contract is R199pm. When i asked about it they said its device obligation carry over, i wasnt supposed to upgrade the contract before it reached an expirey date.i have launched a dispute and still waiting for their response. I cant wait for my new contract to expire i want nothing to do with telkom.