Yeah it definitely sounds off. When I worked in energy we had loads of issues with people switching suppliers because the old supplier would give the new company an absolutely mad read and then give them a refund, they’d move and then the new company would be left to pick up the slack. It’s obvious you don’t owe it from that information so absolutely go through the complaints process and get it to the Ombudsman ASAP. Mostly the Ombudsman won’t take a complaint until you’ve raised it with them for a minimum period which is why I’m telling you to go there first.