Hi evansben and welcome to the forum
Assuming that you have the usual windfall provisions within your IVA, then the £168 will be treated as a windfall - but your IP ought to allow the costs you have incurred to be deducted. If Captial One are a creditor of yours, they will use this to offset against their debt in the first instance.
I am afraid that you cannot really change your IP - this is why it is important for all forum members thinking of entering into an IVA to choose an IP that they feel is going to look after their interests throughout the IVA. It is important to remember that the IP who supervisese your IVA is actually chosen by the creditors, to whom they owe a primary duty of care, but this also means that they must be fair with you as well or else the future of the IVA will be jeopardised if you get fed up with it - to the creditors actual detrient. Most IPs managed to find an appropriate balance. Your IP is foolish to not consider putting forward a variation to your creditors, based upon your recent salary reduction - assuming that none of your other circumstances have changed. Have you considered bankruptcy proceedings as an alternative?
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk