It’s the same for everyone, lead times and not getting a call back is not exclusive to motability customers.
parts shortage has a lot to do with delivery times and not getting a call back could be for various reasons.
I picked up my motability xc40 in December and was kept updated up to every 14 days from order. My sisters both ordered brand new BMWs not motability and didn’t hear a peep from the dealer after order until it was time to pick the vehicle up, their cars were £65k and £50k respectively, so it seems it also doesn’t matter how much money you are spending.
you just have to keep on trying, it is long but it’s the same for most right now.