Just a small point of information

.
Both your phone line and your FTTC are connected inside the PCP (phone cabinet). The engineer doesn't even have access to the FTTC one.
The links are installed at the time the FTTC cabinet is built, with a patch panel installed in the PCP. The engineer just diverts the line to it and picks up the return of the combined signal. So exchange >> PCP >> FTTC (where the fibre feed is - possibly from a different exchange) >> PCP >> you.
What you send retraces that route with the phone and VDSL2 signals being split in the FTTC cabinet .
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
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