Is there a supplier who would change a prepayment to a credit meter?

I Had a key and gas card meter put in a few years ago by southern electric because I'd got into debt partly because they hadn't read the meter for 12 months and partly because I hadn't paid attention. They said that once the debt was paid they would replace the meter's with credit meters. Seems they've had a change of policy since and it'll cost me ?52 per meter all the while I'm paying at least 6% more than people that pay by dd and have paperless billing. Is there a company that will replace the meters if I change supplier? Key