I am in the same situation. Diamond are pushing me to use their credit hire company Auxilis. They say I will have to pay excess otherwise for having my car driven into when parked. And I also have a legal cover.
I called the 3rd party insurer first -MCE, thinking they will be happy to deal with it but they arent and say they will deal with my insurer instead?
When dealing with Auxilis they asked me for the phone number of the driver who crashed into my car so they can call him to find out what happened ( I was on holiday then and another car was involved). I didnt have it, only the address and reg number, but told them he already called his insurance and they will be able to give that to them. They say they cant because they are not my insurer!
How pointless is that? Why cant I deal with my insurer or the 3rd party insurer. No wonder the insurance premiums keep going up.