Bad service

I am battling now for a week just to get a letter from them to get a new nana simcard. I bought a new phone and can't use my old sim card. Vodacom said I must get a letter from them so that I can get my new sim. I don't want to change service provider or my number. All I want to do is to be able to use my new phone. My old phone is giving me a lot of trouble and I bought a new one and now I can't use it anyway. I am going on holiday next week and want to sort this out before I go. Since Monday I phoned them every day and they promise every time it will be sort out soon. I've got a reference number from them as well. Please help I am desperate