Bad service

Upgraded over the phone 4 weeks ago and at the time i was working in Johannesburg i was told that the phone will be delivered in 4 days , days passed it was not delivered i had to move to Pretoria called and gave them the new address they said they will update it on their system.Days passed the phone still was not delivered to the new address , called again to find out when will they deliver they told me that the driver went to deliver the phone in Johannesburg told them that i gave them the new delivery address they said its not updated on the system.Told them to cancel the order and that i will go and upgrade at one of their stores ,the person i spoke to said that he could not cancel and that it can only be cancelled by the person that helped me with the upgrade the first time i called and he said that he will send an email to that person give them my details so that they can call me and cancel my order.its been 4 days now that person hasn't called i'm getting frustrated because i keep getting messages from MTN saying that i should pay the new phone installment tomorrow .How can i pay for something that i don't have.