GAP might be because you'll have chosen a plan for PCP.... call your GAP insurer...
There's only three types of GAP insurance:
Finance GAP insurance - If there's no finance outstanding on finance at the time of claim, the JamesR27's policy would effectively be useless.
Invoice GAP insurance - Aims to pay the difference between motor insurance payout and original invoice price (regardless as to whether there's finance outstanding at the time of claim or not)
Replacement GAP insurance - Aims to pay the difference between motor insurance and what it would cost at the time of claim to buy a new equivalent vehicle (regardless as to whether there's finance outstanding at the time of claim or not).
There are then policies which are combinations of the above. E.g. a combined Finance & Invoice GAP insurance policy would aim to pay the difference between your motor insurance payout and the higher of the amount (if any) outstanding on finance at the time of claim or the original invoice price paid. Etc etc
In short though, JamesR27, you settling the finance early shouldn't have any bearing on the GAP or service plan that you bought from the dealer if you've already taken delivery of the vehicle.
That said, if you *did* buy GAP insurance from the dealer, you've almost certainly paid through the nose for what is probably Invoice GAP insurance at best. I'd be looking to cancel it within your initial cooling off period (at least 14 days, but usually 30) take a refund of what you paid for it and then buy a better (e.g. Replacement GAP insurance), far cheaper policy online from the likes of
GAPinsurance.co.uk or
ALA.co.uk etc
HTH