Summer Sun Trading not delivering the device ; Option cancellation

This company upgraded my contract on my phone no. ********** 105 in August 2017 and promise to send me my phoning device . The co. never send the device up to this moment. I have enquired for a number of occasions but in vain. I opted for cancellation of the upgrade they are not doing it either, after six months pleading with them to cancel the upgrade. in the meantime I am paying for the servises with MTN R1500. MTN is saying they are suppose to cancel the upgrade if they are not delivering the device. Can you assist in telling them to cancel the upgrade so that I can be purchacing the device with MTN directly.