Unable to resolve customer problem

I took out my contract with Cell C March 2015. Ever since I have unresolved problems. I have sent my phone in for technical repair that took 3 weeks. I had a software consultant visiting my home to establish signal strength. I did software upgrades numerous, and very limited reception after all. 40- 50 % of the time I have reception, during this reception I can only make and receive calls for duration of less than 30 seconds. I loose signal and the conversation cut off. The latest now I the last resort I was advised to do sim swop as the problem could be with my blue sim as I was explained the blue sims cards give problems. Week 1 I was told no stock of the black sim cards. I should come back in a week. A week later 24/10 after spending an hour in the store giving details of my drama my reason for the sim swop and extensive security questions I was told 24 hours the swop will be done being a weekend. Tuesday I got a call from the call centre, after 15-20 minutes during working hours I again was asked extensive and irrelevant security questions ridiculous details. I was then informed that the sim was already registered to another number and my sim swop cannot be done<br>