When I bought my 1996 Catalina 28, the main was difficult to raise, and the halyard came off the roller and got stuck, just like yours. As others have suggested, it's probably the sheave. They take a heck of a beating from the UV up there on your mast.
My boat was new to me and I didn't have a system for going up the mast yet, so I took it to the yard and they accessed the top of the mast with their bucket crane. If you have a yard with one of those handy, that might be your easiest/cheapest way to replace the sheave.
Of course, while your at it, definitely have the yard replace all the sheaves. When I did mine, I ordered the sheaves online and gave them to the yard, just to be sure they had the right parts. I used a ball bearing sheave for the main halyard (gets used often), and for the less used halyards, just regular plain bearing sheaves. Either way, the sheaves don't cost a lot. Been a couple years since I had it done, but it probably cost around 300 bucks.
You really need to know what's going on up there.