So have you fitted the connects2 adaptor lead linked to earlier?
I would have thought that would sorted out your FM problems
, the single blue wire powers the FM amplifier inside the metal box part to boost the signal, your current 2 aerial fakras plug in twin blue socket end, and single silver FM plug in back of head unit.
There are many types of VW aerials, with many different lead connectors.
Failing all else you may have to take to VW dealer
or let good car audio shop sort it all out for you.