OP, I'm really sorry for the problem you are having with your reservations. I hope they can get this fixed with a satisfactory resolution.
This is very strange. In the past when I have tried to get 2 reservations from 2 different contracts (different UY's) linked together at VGC and I was told there was no way- no how they could link them. This is something that is quite commonly done at WDW
DVC resorts, but member services always does it. They always say--it's only a request which may not be granted and you still have to check out and check back in (and there are still 2 reservations--they just make a note in each reservation).
The reason I link reservations is because I want to stay in the same room and not have to move. But, as noted there are only two 3-bedrooms at VGC and each room has its own booking category (IIRC the accessible 3-bedroom is the one that faces paradise pier and the other 3 BR faces the pool). So, if booked in the same booking category--it would by default be the same room. If they were going to do anything, I would think they would just make a note in each reservation.
Who did you contact at the Grand Cal? I didn't think they (Grand Cal) could cancel a reservation except last minute and when member services was closed? (I always get referred back to member services). Unless as Sandisw mentioned, there is another reason such as the room is being taken out of inventory for some reason. (But, I think it is strange to be taken out of inventory 10 days in advance--unless it was a scheduled refurbishment--which I didn't think started this year?)
Did the reservation disappear from your dashboard?