5 months with no internet

[#1]

We have had ongoing issues with drop outs for the past 5 months. We now have not had broadband for 2 weeks. I ring Plusnet almost daily to get the problem resolved and nothing gets put into action. We have had 3 engineers out and they can find no problems with the line even though our landline has so much static it's almost unuseable.
We have been promised refunds but nothing has been refunded. I've made official complaints yet nothing has been logged. I feel that Plusnet are happy taking my monthly fee and just ignoring me and my problems.
I do not know what else I can now do, anyone out there recommend my next course of action?

[#2]

Hi there.

Apologies for the ongoing connection issues you're experiencing.

I can see we've raised an escalation with our suppliers. Unfortunately we've been advised we need to book another engineer visit to further investigate this, but once booked we'll request that this is escalated with Openreach.

Can you reply to your ticket here with your availability and/or the text message I've just sent?