Ive had the same problem, and ended up with a Doctor in Sydenham! Mostly it was because they couldnt find my address on their map (I had moved into a new development) and couldnt reconcile that with the address list they had as it was most likey not updated with my address. Stupid really, it meant that someone living about 20metres away from me and further from the surgery was on the list, but I wasnt!