Donot Invoice people... *****ing Money

I exchanged a hanset on the 5 September 2015 from the N1 city walk in store. Firstly I was told that the phone that I was exchanging is discontinued and that I would have to pay in a differen(There handset was faulty). Didnt mind had to get it sorted. Then the Guy (Russel) says the diffrence is R350. How can it ever be that the old phone cost R449 and the New one cost R599 that the diffrence can be that much??? Eventually he agrees that we must pay R150 which we did in cash. He then says the system is offline and that he can not issue an invoice and that he will email it to me Monday morning. STILL WAITING... I contacted the call centre they escaled the matter with the store manager a week later no response. In my opinion they are a bunch of ******* that ***** money. The Reference number for my complaint is SRET***