Hi Dave
Something strange has happened here. The equity point should usually be dealt with at month 54 of the arrangement so somewhere in 2012.
Given you received confirmation about your final contribution and it sounds like you have heard nothing since in 3/4 years I would suspect you are within your rights to make a complaint here.
First check whether you are still on the IVA register here:
https://www.insolvencydirect.bis.gov.uk/eiir/
I wonder if this was overlooked by GT and now they are having a review of dusty old cases following becoming Aperture and this has only just been picked up.
At the very least the valuaiton should be based on 2012 prices.
See if you can a) argue its been 4 years and they've missed the boat and you will make a complaint if they don't close your IVA
b) that your equitable interest was less than the £5k in 2012 so the extension/remortgage won't apply anyway.
Absolute worst case scenario- if none of that works (but I would hope 1) does), will be to find monies to make a settlement offer towards a further 12 months of contributions.