You should try and offer as close to the original amount as possible but you can but try to make your offer. Don't forget you will have fees to pay on top and it will take a couple of months to go through.
The debts included in your IVA will be cleared but the other ones won't. Not sure if you would be able to do a DRO but you could go bankrupt. You would have to pay for it (can't remember the fee now) and you may have to have a payment for three years but you would then be cleared of all debts.
Very bad of your company and I would certainly make a complaint! You could try again with a different company? In the meantime try doing a Debt Management Plan. This will keep the wolves from the door for a short time.