Thought I'd share this with anyone who might be thinking of giong through the same thing
Just received a cheque today from onestopphoneshop for £350 for cashback they refused to give me.
I claimed for my cash back correctly as i like to think I'm a fairly intelligent person but they refused to pay up (they wouldn't give me a reason to why they wouldn't pay). So i had to go through the small claims court (all on-line now). OSPS actually paid their solicitors to put a defence in (still wouldn't give a reason why they wouldn't pay just said they didn't owe me anything). So it was all set to go to court when they sent me a cheque for £109.
However, they refused to pay the rest of cash back claim so i had to go to court again to get the remaining £350. This time they didn't even bother responding to the court so i automatically got a judgement in my favour allowing me to ask court bailiffs to recover the money, but they paid up after i sent them a letter threatening them with bailiffs.
So I've ended with all my cashback for 12 months (only 10 months into it), plus £50 costs.
So anyone going through the same crap with OSPS its easier and feels a damn lot better just to take it through the courts. All in all its taken about 2 months from start to finish. If anyone needs help going through the process just let me know.