As Licquorice said, the old copper should be perfectly adequate.
This sounds like a disgraceful load of nonsense in order to squeeze money out of the vulnerable!
Back in the old days of the old rubber-based insulation, the operational life of mains cabling was about 30 year but that's not been used in my lifetime, (and I'm knocking on 70). I doubt whether it ever applied to phone cable and it certainly doesn't since PVC insulation.
I recently sold my mother's house after she passed away. That phone line was put in when I left home at 18 . I can't answer for the overhead line, but I know for a fact that the 10m from where the line entered the house to the master socket had never been updated. In other words, it was about 50 years old! Didn't stop her getting FTTC, which worked fine. (It was still old figure of eight cable, in fact. It's actually thicker and probably a better conductor that the modern stuff and, while it doesn't have the cross-talk resistance of twisted pair cable, it worked fine at 40Mb/s).
And Digital Voice (DV) also works fine over copper. It doesn't need Full Fibre. My own house is nearly 40 years old and still the original wiring. DV worked absolutely fine for two and half years until I upgraded to Full Fibre.
