Wrong device delivered - no cancellation of contract

I telephonically upgraded my cellphone contract with Summer Mobile an MTN Dealership. my contract package was an Samsung Galaxy S8 + Samsung J5 pro. Onthe 21st of November 2017 only samsung galaxy s8 was delivered. I called summer mobiles to notify them about the wrong order i recieved. They advised me to it back to my nearest MTN store to obtain a ref no. I took it to MTN liberty mall in Pietermaritzburg. I then called Summer mobiles i spoke to Kate and give them the ref no. And they promised to have my contract cancelled in 24 – 72 hours. As from there I kept on following up my case, summer mobile consultants kept on giving empty promises to call me back and update me. Non has ever called me Ive wasted too much money buying airtime to call them. At times they would hang up on me. Asheelne the summer mobile supervisor also promised to get my contract cancelled but it has not happened. And now not responding to my emails. on the 19 december 2017 i called summer mobile and spoke to Noma who said to me is contract will be cancelled the next day.

Today the 3rd of January 2018 my contract is not cancelled, the device is not with me and Im paying for it monthly.. Please help me