not taking cell phone still under warranty

i purchased a blackberry Z10 from jet in jabulani mall on the 25 may 2014,the phone is not working well so i took it back to the store that i bought it and they told that they cant take the phone i must take it to MTN.went to MTN and they told me i must take it to jet as the phone is still under warranty or pay the admin fee of R300 for them to book the phone for me,i went back to jet and they told me they dont take the phones anymore and i must go pay the admin fee at MTN.this is unfair treatment on my parth because i am sitting with a phone that is not working and its very inconviniencing for me.according to the slip that i have i must take the phone to jet because it is still under warranty.the communication between the two companies is not clear and the message tghat is given to us is in correct.