I can 100% promise that if the original poster were to switch to DV this problem will naturally be resolved as it has done for me.
But with FTTC VDSL the copper connection between the cabinet and modem is analogue. One could say, with 100% certainty, that the unknown fault with the copper line would obviously no longer be a concern after a change to Full fibre FTTP. However this is currently not an option for the OP 
As I have said I'm on copper with FTTC. I don't have Openreach FTTP yet.
If the problem with the copper line (broadband disconnecting) is only triggered when the analogue telephone line rings, picked up or connected and disconnected from the master socket then Digital Voice with FTTC will solve this problem.
What I'm saying is if the OP is not having general broadband disconnections with his copper line but this is only happening with the phone ringing, picked up or connected and disconnected. Then Digital Voice will definitely solve the problem.
I didn't have general internet disconnection related to noise margin when I was with TalkTalk FTTC. But with TalkTalk FTTC only offering analogue phone line, I had this problem for 2+ years.
I then joined 13 months ago BT FTTC Home Essentials 2 with Digital Voice. During the signup process I was given 2 options. To remain on analogue or to switch to the new Digital Voice service and I'll receive an Advanced Digital Home Phone with Alexa built in.
I opted for Digital Voice and received this new Digital Home phone along with Smart Hub 2 router. The phone is wireless and only needs to be registered to the router once by pressing the WPS button on the router.
As soon as I migrated from TalkTalk to BT 13 months ago I noticed that plugging and unplugging the traditional analogue phone wasn't causing internet disconnection! I then checked for dial tone and noticed that it was silent.
This indeed meant that the transition to digital voice from analogue is actually what solved the problem for me. This naturally resolved my disconnection problems because as soon as I tested by calling my own landline phone number with my mobile phone the internet connection was not interrupted! I did several tests to confirm that this wasn't just exceptionally not occurring.
I then made an experiment and plugged this vintage phone into the router and it worked, dial tone was working!
Currently only a few ISPs on FTTC offer Digital Voice as a service and BT is one of them. If this disconnection problem is happening and it is only being triggered with analogue phone then I can 100% reassure that Digital Voice migration will solve this problem permanently!
But this means you are restricted to only a few ISPs that offer Digital Voice with FTTC until December 2025 when all ISPs will migrate to Digital Voice.
Edited by BLaZiNgSPEED (Sun 13-Aug-23 19:12:34)