If your broadband service has been activated or regraded, and if your line speed is lower that promised after 10 days, then you are entitled to a free visit from an Openreach broadband technician to fix the issue, but you must report it right away.
Repeated disconnections would also cause the line speed to drop, so the cause needs to be investigated.
You must report the slow speed within 90 days of your service being activated.
See Early Life Failures - moderator post
If the above applies to you, then please reply on your existing BT forum thread, or start a new one, so a visit can be arranged.
Action to take when download speed are dropping during peak times
Do not attempt to cancel if your speed is not as promised, please follow process as described on this page.
Cancellation of your service will be subject to the following conditions:
You will be able to cease without penalty if BT is still unable to improve the speed measured by the BT Wholesale speedtest above your Minimum Guaranteed Access Line Speed.
The Minimum Guaranteed Speed relates to line speed only, not to download speeds.