Can you give us some more details? Why do you think the company is charging too much?
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
It probably depends on if you are asking them for the balance, in which case you will always owe the full amount of your debt + fees (around 15% or more) + interest (8%) less the amount you have already paid.
OR you are interested in knowing how much you can offer to make a F&F payment to end your IVA with money being offered from a third party (ie friend or family, etc), which would usually be the monthly amount you normally pay X the number of payments left to pay (including any extension due to equity). This "offer" can usually be reduced slightly as the creditors may prefer being paid as a one off up front than an extended monthly arrangement.
As Kallis says, more details and the reason would be beneficial.
Where will you get the funds? How much will you pay if your IVA continued to its normal end date? Do you have a property with an equitable interest in it?
Your IPs charges were approved by creditors and effectively come out of their pocket/reducing their dividend so unless you are paying 100% of the debt plus interest plus costs in full it shouldn't really affect you.