Gas Paygo Debt

cardiffforthefacup

This is my problem, I got a letter today from SSE gas asking to contact them, basically I owe £637 from November 2008. Don't know what to do or my rights but I am with Ebico for gas which was on a payment meter where I paid weekly approx £3. So this amount is a total shock!!! Anyway the gist of it is an error took place that switched my meter to a credit meter (quarterly billed), I received a letter with a card (prepay) and it said that if I wished to stay as a credit customer to do nothing and they would send bills each quarter. I phoned up at the time to confirm this. However one thing led to another and being depressed never chased them up for bills so today got a letter. so now they want £4 a week (they asked for £15) which I haven't got with all my other bills this would leave me severely short. What is my position, would I be able to get a crisis loan for this amount or am I stuffed. I have a daughter of 15. Can this debt be written off as good will? or am I forced to pay it back despite them not contacting me since nov 2008