Okay, an update: I'm now with Madasafish and everything went very smoothly. I'm paying my less than 10£ a month and don't have the hassle of a quarterly bill anymore, but a decent and nice monthly bill. My broadband is still with O2 and it didn't matter at all that I changed from BT to madasafish. I highly recommend them and their customer service is really good.

Regards,

Mat