As OG correctly suggests, a customer can contact the appropriate ombudsman for energy disputes; OFGEM (sic) will not deal directly with individual customers as its job is to regulate the industry.
There is a specific band of issues the ombudsman is mandated to deal with - here:
http://www.ombudsman-services.org/what-can-we-deal-with-energy.html
If such a dispute reaches deadlock, this is where your MP can come in handy. Twice, many years apart, I have been in dispute with a power company, both times I was in the right, both times the company concerned refused to listen to reason. In both cases (different) MPs contacted the Managing Director or CEO and the bother was settled with a day or two, literally. In one case I got compensation.
We had a dispute with an electricity company (can't remember which one) and took it to the ombudsman - it went on for ages. Had to write lots of detailed letters, stressy phone calls, etc. (but we 'won').