If you have problems with your BT broadband connection or speed, there are a few checks that we recommend you carry out before calling us. These checks can help you resolve your issue, or at the very least help you eliminate any internal wiring problems that could be impacting your service.
We would also recommend trying a different filter, if you have one connected. We would also advise accessing your test socket, to bypass any internel wiring. That check is outlined here, where there are a few helpful videos that visually explain how to carry out the check.
If you have completed these checks and you are still having issues, please contact us on 0800 800 154 or contact one of our livechat teams here. 
Regards
Ryan