my money lost on this branch

About a month ago my BlackBerry z10 started to give me problems.I was advised by Cellc customer service to take it to any Cellc store for a software upgrade. I went to Newtown junction and was assisted by a guy called Phinda who told me I will be charged R150.00 which I gladly paid and the phone was Ok when I went to collect it the following day.After only 2 days of using it it gave me the same problem again. I went back to the store and was advised to rather book it for repairs by Cellc technicians which I did.I then demanded my money back from the said person seeing that my phone's issue wasn't fixed properly.he promised to pay me back my money but up until now hasn't done so.I always go to that store but the staff there including his manager Celiwe Radebe are telling me that they don't know his whereabouts. I feel offended as I have been loyal to this company for over ten years.I trust that I will be helped and action will be taken. Frustrated customer