Unfortunately, copper doesn't have the advantage of a super fast light connection like Fibre. As such there are a number of things that can cause a VDSL connection to not perform as expected.
Take a look at your router, there should be a cable inserted into the grey DSL port. The other end of the cable should be directly plugged into the existing wall socket you have.
Make sure you don't use any filters or have anything else plugged into the wall jack. There should only be a single cable between the wall jack and your router. In addition to this, make sure your other wall jacks around the home have nothing plugged in as this may interfere with your connection.
Your connection should look similar to this:
Has this resolved your issues?