BRAND NEWBLACKBERRY BOOKED IN 3 X IN 1 MONTH

My first 9720 BB I received on contract on 6/03/15 - on 16th it stopped working apparently i broke the back sim pin which i could not know as its a brand new phone but i told them okay fix it please as the phone is 10 days old - they could not fix it and told me its broken i had the option to buy a refurbished unit for R850 i got it only on the 27th of March, now this phone only worked 8 days I had to take it back because all calls could not hear me but I could here them 100% like 3 minutes into a conversation - then they fix the problem and sms me that the phone is ready for collection which i picked up on 10 April 2015 - i took the phone back yesterday as the same thing still happen NOTHING HAS BEEN FIXED. My new contract started on the 6th of march - its the 15th april & still no new phone that works for longer than a week without issues. i know i signed a contract which i am in debt to for 24 months - i did ask the vodashop that i NEVER want a 9720 again i will pay in extra fee ontop of R850 for refurbish 9900 / 9810 BB but they say its not up to them to give me a diff model than 9720 this is sad and very depressing for a new deal, or refund me the R850 i will buy a 2nd phone