Hi pop
This is a difficult one.
Ark Life made a mistake in not cancelling the policy when they issued a new one for the first remortgage.
Ark Life made a second mistake in not cancelling both policicies when they issued the third policy.
However, you should have noticed the money coming from the account earlier and you should have corrected their mistake.
Had you died, your estate would have benefitted from the extra insurance.
I think you should put your complaint in writing seeking a refund of all the extra money paid. They will make an offer to you. If you are not happy with it, then you can go to the Ombudsman.