Before you go to the FSO ask the Vulture fund on what legal basis are they charging you the 4K.
Vacate Fees
In relation to Vacate fees, used to be about 50 IEP. But Ulster bank no longer charge it as there is a new procedure as far as I understand it, meaning no need for the vacate fee. Vacate fee was a charge for getting the name of your bank off your mortgage title when the mortgage had ended.
Early redemption
This is when you decide to pay off your mortgage earlier, or sell a property. Your bank gives you the redemption figure to be paid. Never heard of a charge for this until today. Maybe a small admin charge but nothing like even 1K never mind 4K.