I guess your ex wife thinks you will not return her ! Best way is go talk to you ex wife and try work it out. Lawyers will cost a fortune and take forever with no guarantee you will win. Go talk to her and blow fliers up her ass
Don’t use agents it’s easy to do yourself. Make sure you answer all questions correctly, Show you can keep her ( money wise ) show she has her own home and a job to go back too. I done it twice. And no problems at all. ( last one took 2 weeks. , em/ year Multi entry for my Thai gf to Uk )
Do it I line, make sure you give as much I do as possible as it’s done thru an agency first. Stare the obvious. Show that gf has a job ( and a home if possible) get a letter from her employer. Show you have plenty of money to keep her , I got 6 month in 3 weeks then a 2 year visa that took 2 weeks , you need to show she will return after visit.