The form you filled out when you sent the money had carbon copies, which are retained. If data from the form was mis-typed later, they should be able to check their copy, or you might be able to retrieve a copy from the outlet or receiver or something.
I assure you that no-one in WU is trying to steal $50 from you. Mistakes happen, but there is a paper trail, so if you really care, escalate. They operate under the supervision of your country's financial regulator, whom they are deathly afraid of, and are hardly going to risk their banking license pilfering fifty bucks.