What I and most on here have called the hitch is actually named "coupler". There have been many different types made and still used on RVs. Without showing the coupler or telling us what trailer you have, we are just guessing. The only other helpful advice I can give is, make sure the ball and the coupler are the same size. Both have the sizes on them. It would not be the first time I seen or read about folks using the wrong size of ball and coupler. Good Luck and let us know what you find that works.
2013 24RKSWE (27ft TT) Cougar 1/2 ton series
2013 Ford F350 4x4 CC 6.7 engine, 8 ft bed 3.55 rear end lariat package
Retired from Oregon State Police in 2011 than worked another 9.5 years as a small town traffic cop:
As of 05-2020, I am all done with 39 years total police work. No more uniforms for me.