You need to have already put in a complaint through BT about it, the sooner the better if not already done it.
https://www.bt.com/help/contact-bt/complaints
If that doesn't stop it then you go down the Ombudsman route and you get them to stop it
As stated on BT Complaints, you have an eight week window in which BT should sort your complaint out, or if not happy with their outcome you progress further yourself.
What if I'm still not happy?
You can contact the Communications Ombudsman to investigate your complaint if we haven't solved it within 8 weeks, or if you're not satisfied with our response. The ombudsman is free, independent service.
https://www.commsombudsman.org/
However this could be a lengthy process and you'll need enough evidence to back up your case and how it affected your BT service and how it affects you personally and financially.
Note that the Ombudsman route may give you compensation due to losses occurred, however that is at their own discretion after judging on the case, and if they know that BT have already refunded you, then they might not do it.
Be aware that as it is a residential line then the Ombudsman will most likely just look at the service provided by BT here and rule purely on that, and not take into consideration any financial loss personally on your part, etc.
The fact that they will clearly see BT have refunded you every time, might mean that whatever official and binding ruling they give, it might just end up with you having a token amount as compensation from BT.
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