Hi Yissy, Hope your mare recovers soon, I'd be pretty upset if this happened to one of my horses too.
In my training career I have taken on two "geldings" that were cryptorchids (ridglings) and the owners didn't realize it. This is when an unscrupulous vet removes only one testicle when gelding. One of these horses was actually a registered
This causes the horse to act very much like a stallion and is very dangerous especially for newbie owners. In some cases
these horses do retain some small portion of fertility
One of the clients did the right thing and had the surgery done to complete the gelding even though the horse was older and had a hard, long recovery. The other client sold her horse immediately to an unsuspecting buyer who didn't have a clue as to what they were getting.
I actually bought an ungelded colt knowing he was a ridgling and got the seller to drastically reduce the price on him. The surgical gelding cost me $600.00, a stay over night at the clinic and antibiotic shots for 10 days.
This "gelding" may very well be only partially gelded and capable of fertilizing your mare but don't expect the owners to be honest about it. Or they may not even realize the problem as these horses are sold to unsuspecting buyers all the time.
I suppose you could try sending a letter to them along with your vet bills and see what happens. There is always small claims court which doesn't require a lawyer if you would want to try that. Good luck!