Hi MalNCH
Sorry to hear you are having these issues - whilst this is not something I have come across myself, it is certainly something I will do my best to assist you with.
I think getting in touch with Openreach is the right way to go with this one. They have clearly not been very co-operative however as evidenced by your lack of reply from them. What I would suggest is getting an Openreach complaint raised - that would at least help you get this sorted with a bit more urgency. You may have to do that via TalkTalk, your service provider.
I hope you have some joy with this!
Regards
Ryan