I had a similar issue slightly more recently, (still not quite resolved, though I've been promised it will be). I raised a complaint online but heard nothing for over two weeks.
So, you could try emailing them or phoning BT. (The first call I got back wasn't much help - tried to claim the offer I'd seen wasn't running on the date I saw it, despite me having read the small print and checked the offer dates the day I ordered - I only got a promise of a resolution after escalating the complaint and getting a second call back.) Hope you don't have the same problems!