Bad customer service

I took a contract with MTN Jabulani mall, blackberry 9720 the phone had problems I took it back got a new one still had problems, they gave me a third new one but still it had problems and i had to wait 3 weeks for the 3rd one, when I took the last phone back they said they will order another 1 for me but I haven't received a call to say come fetch your phone and its been 3 weeks now or two. I am tired of dealing with MTN and i do not want the phone anymore, sad part is am paying and with 3 phones being faulty within 2 months of the contract is not good. Please assist to find a better solution to this because I cannot deal with them, I have had enough. The contract number is *** which is off because I do not have the phone.