You said that you paid in full for arrival/departure at Club Mobay -- were you issued a refund or did they never charge your credit card in the first place?
Also, am I understanding correctly that you tried to book Club Mobay through Hedo? If so, I've never done that -- I've always booked directly with Club Mobay and left Hedo completely out of the picture (as you may have figured out by now, Hedo can sometimes be rather unreliable. One of my Hedo friends used to book his vacation directly with the resort -- until one year when they lost his reservation and he missed his trip! He never made that mistake again.)
From what I've been hearing, it's been something of a challenge to book Club Mobay these days. My trip isn't until end of the year and I booked Club Mobay back in June!
I've been booking Club Mobay for the past several years and found the service to be quite good. If you're not using them this time around, make sure you complete the Immigration/Customs form online prior to your trip; Denny has a link to that here: https://dennyp.com/Jamaica/immigration_info.htm
My recollection of the pre-Club Mobay days is that on arrival, be prepared for standing on very long lines for quite a while (may be true with departure, too).
One other thought: it's possible that between now and the time of your trip, a spot may open up at Club Mobay -- if that occurs, you might be able to book with them right at the airport.