As I mentioned, MARSHA (Marriott's overall reservation system) can oversell a property. I've got friends who work at MAR properties & they want to tear their hair out when it happens because they know at the property level they're fully booked & will have to relocate guests. The oversell doesn't usually happen a month or so in advance (if it had you would have been contacted then), but often close to the date. Also, there are things that can happen that can cause a room(s) to go out of service, which means the property doesn't have all the rooms it originally sold. If the property is saying it's oversold, then it's a MARSHA issue.

I thought Al Maha switched that award bookings were room only & not all-inclusive. I thought the switch was at the start of the year for the change, so if you booked in the 3rd week of January, even though the property is all-inclusive you might not have gotten that. I'd have to read the property thread to find out when the exact change occurred, but if you read the property thread you'll see about the changes. If your reservation was made before the property switched to room only & not all-inclusive (on award stays) they should honor the all-inclusive part. If your reservation was made after the change, then you're getting the room for free but the other stuff would cost $$, in which case getting another Dubai property would be somewhat similar.

At this point the point the property has told you that they do not have a room for you. So the next best thing is to tell them that you expect them to book a reservation for you at a property that's as close to comparable as you can get for the same amount of points. You can also ask them for a lot of additional points to make up for the inconvenience.

Alternatively, you can talk to them about changing your reservation to a future date & contacting the airline to switch your plane reservations to a future date. While the airline tickets might be non-refundable, often the airlines will waive fees if the city/country remains the same & it's a simple date change. While not ideal, pushing your holiday to a different time & then going somewhere else might work out better.

Good luck!