OVER CHARGED FOR PHONE REPAIR

I took my phone in for repairs on the 29th May 2015. The problem with my Nokia Lumia 720 it would switch on, cracked screen, also required a soft ware upgrade. I then requested them tp provide me with a quote they the called me on the 3rd June and told me that to get the phone switched on they charging me 400.00 software upgrade 400.00 to fix cracked screen is 1000.00 I then said to the that is too much they must not fix it then because I'm due for upgrade July 2015 I jusy want the phone on to be able to use it. They said I must then pay the 400.00 just which I found it rediculous I feel that th?y've overcharged me my phone is a contract. I then called Vodacom Cusotmer care in Westgate related my problem was told told to 120.00 and a memory stick to keep whatever information I need on my phone. Please advise where can I take this up I paid 400.00 for nothing please helpme get my money back. Your prompt response will be highly appreciated.