Closing an InvestEngine ISA

I had a small amount in an InvestEngine S&S ISA but withdrew the money to a zero balance (no risk of paying tax etc) and now wish to close the ISA.

I emailed support and they said I am unable to do so because the portfolios I created have transactions on them and the FCA require them to be kept.

I get that records need to be kept for regulator purposes but surely transactions on an account shouldn’t stop me being able to close the ISA? Otherwise anyone anywhere who’s ever paid into an ISA wouldn’t be able to close it!

Anyone else had this issue?