I had the same problem with phones 2u direct & eventually my network provider (02) sorted it out for me.

Don't be put off by customer services telling u that it's nothing to do with them. Insist on your complaint being escalated to the serious complaints dept. I was informed that network providers would black list any company not complying with the agreed terms of cashback & they are in a position to exert pressure on phones 2u direct & other such companies. 

Good luck