I'm not sure that what is going on is wrong - or indeed Q jumping.
The bottleneck in the whole process at one point was the supply of the front roof panel, this has now been resolved I understand and the bottleneck has not moved to the loan vehicles. My understanding is that a loan vehicle is send out, swopped with the one to be returned and taken back to the repair facility. This takes some time, at least a day but often more. Then the whole delay is repeated when it comes to returning the repaired vehicle. During that time the repair facility is sat waiting. If an owner is happy to give up the right to a loan vehicle then the low loader can be sent out when it would otherwise be sat idle and ensure that there is a constant stream of vehicles available for repair and hence the whole backlog can be dealt with much faster.
The question is wether a loan vehicle is required or not. Yes we all have the right to it, but to exercise it will slow the process down. The repair facilities are offering the chance to have your vehicle repairs quicker if you don't need the loan vehicle.
In my case, AB Crush phoned and asked if I needed the loan vehicle. On balance, I decided that I didn't real need it, it's only away for just over 2 weeks and it will be in the winter - so if anything it saves me some space on the driveway. Maybe Heritage aren't phone people in the order that claims have been registered and are just dealing with people that are proactively asking to not have the loan vehicle?
It some ways, I've been keep to delay the repair - it's not stopping me from using the vehicle, and the later it is done, the new it will be for longer should I wish to sell and further more, that's a change of getting a newer modified bellow fitted.
I think the only real reason to push would be if you were planning to sell, it would be easier to sell with the work having been completed rather than a piece of paper saying that it will be done.
In the meantime, enjoy the freedom.