Second Charge still on deeds after it was paid off!

Hi, back in 2006, my wife and I took out a Firstplus loan, (to run with our Northern rock mortgage) securing the debt on our house. This, naturally, led to a second charge being put on the deeds at the Land Registry. A year later, 2007, we were in a position to pay off this loan, which we did, and received a letter from Firstplus saying the second charge would be taken off within 28 days by their solicitors. That was that, fast forward to 2019, because NRAM (northern rock) now don't offer new deals, we are in the process of remortgaging to another lender but everything has ground to a halt because Firstplus never removed that 2nd charge, 12 years ago! Weve been too-ing and fro-ing with the company which took over the Firstplus accounts, but they seem to be really dragging their heels over it. If we lose the mortgage offer because of the time taken, can we take legal action for 'administrive negligence'?