mondo and telkom service sucks

three weeks ago mondo called me for a contract with Telkom. so I took the contract because the deal sounded nice and I needed a phone. when the phone came the first day I started using it it made blury lines and jst kept switching off. I called them and they collected the phone. mind you this is a new phone that I never used and instead of them replacing it they decided to send it for "repairs" which I didn't agree with but they said that it is their process. however two days ago when I got the phone back same thing happens and when I called to cancel my contract they tell me I must go to Telkom and cancel with them or ask them to repair it, when mondo is the people that called me. I have gotten no use out of this phone and but yet I am expected to pay. all I want is for them to replace the phone with a new one or to cancel the contract.