How to redownload software that's already installed

3 years ago, I downloaded FilmForth video editing software. I paid for the premium version so it wouldn't have the watermark and offered more. I had issues with the software last year so I thought if I would delete it and redownload, it would be fixed. Now it's asking me to pay for the premium again. But when I put in my information, it tells me I already own it. I contacted FilmForth and they said to contact Microsoft to fix the issue (seemed to be a computer problem, not program they said). I've contacted Microsoft and was directed to 7 different people in 4 hours, and even had 2 different people take over my laptop to see how to fix it. I was told to contact FilmForth to see about them fixing it.

I'm just trying to get the software back.