NowTV not paying refund

Acespok

I left NowTV as my broadband provider two months ago. There was about £5 credit on my account. They have not refunded it. I phoned to ask why and was told there's a problem on their end with processing payments. For two months(!)

I have submitted a complaint through their online form. Is there anything else I should do, or can do after a certain amount of time?  I know it's a small amount but I suspect that's why they do it - over all the accounts they do it to it'll add up to a lot.  It's a scummy business practise I don't want to let slide.