Andrea,
The £2240 you have paid to Thomas Charles is basically a broker's fee for packaging the information and appointing an IP.
Therefore if you went 'direct' to an IP it wouldn't necessarily cost any more.
However I would agree with the other posts that your best best at this stage is probably to stick with TC/Accuma.
If the IVA fails TC offer to refund the £2240 plus £250 on top I think, giving you a good basis to restart if needs be.
However at the end of the day Accuma probably won't have any greater or lesser chance of getting the IVA through than any other IP and it seems your chances are good, having an excellent offer even with the awkward creditors.
In terms of your comments about the interest, I think regulations which apply to the early settlement of loans to reduce interest don't apply in default cases unfortunately.
-Best
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