Hi. I work in car insurance claims so i think i can help here. The other driver's insurers will ensure there was sufficient reason for the delays on repairs. If there isn't they will refuse to pay the full cost of hire. At no point will you be liable for this cost though.
For your second question, there is an ombudsman but they are only there for customers who have made a justified complaint to their insurance company, but are not satisfied with the way their complaint is being dealt with, not if you're not happy with their decision. In this instance the only valid complaint you may have is the delay, but I would be surprised if there wasn't a reason for that, because all parties involved would want your car repaired as quickly as possible, especially the garage.