krens29: Do you think they are trying to cover their backs here? Just seems a bit fishy to me...
I think you are *probably* being told what the customer adviser can see on the Customer Information System. If so it has no bearing on the reason for the original scr*w-up, and the facts presented are certainly consistent with a meter or account registration problem, a qualifying reason for unbilled consumption more than 12 months prior to the present being waived under the regulations.
You need to make whatever case you wish to make. I would give the SWALEC customer adviser one more time limited opportunity to resolve the issue to your satisfaction. You might as well demand "the works". If you are not satisfied, submit a formal complaint strictly in accordance with the SWALEC code of practice on complaints. After 8 (or 12?) weeks if you remain dissatisfied you are entitled to refer the issue to to the Energy Ombudsman. You may wish to discuss the issue with Consumer Direct. A particular point about the Energy Ombudsman sceme is that it will be well versed in demanding documentation from SWALEC which descibes the chronology of the issue. Also it costs you nothing.
You might also consider making a £10 Subject Access Request of SWALEC requiring provison of all data they hold on you include copies of bills, correspondence, call logs and call transcripts or recordings. For £10 it's a no-brainer.