For FTTN, the 1st port of call in this situation is to make sure the wiring in your home is up to scratch. Have a qualified cabler:
- Make sure the ADSL central splitter is removed if one is installed
- Get a single line installed from the lead in directly to where you want your VDSL modem to be placed to eliminate any interference that existing wiring may be causing.
- If you can't get a new cable installed then ensure all extensions (taps) are removed so the result is a single line to your modem
Many people have seen exceptional improvement in performance by remediating their wiring. A professional cabler will be able to do a test before any work is done to see what kind of improvement you can expect. They do this by testing the line from where your modem is plugged in and then again from where the lead in enters the premises after disconnecting the internal wiring.
Have a read of this:
FTTN/VDSL2 - results from improving in home cabling - “NBN” - Whirlpool Forums