Well, I’m confused, but I remember the various flavors of verbal horse riding agreements that flourished among my group of teenage riders, long years ago, so I’m going to treat this as if it were one of those.
You never signed anything so you can politely let them know that you are going to end your verbal agreement and seek a rideable horse.
Unfortunately with that kind of agreement, if you wanted the vet out you had to call the vet and pay extra yourself, and sometimes the owner/custodian/person who was taking your money wouldn’t cooperate regarding the need for a vet visit, they’d argue and tell you the horse was just fine or they’d be forever unavailable for any time you proposed, etc…
If you wanted to make a difference for the horse, I’m sorry. Sometimes you just can’t as a non-owner. You can throw all the money you want at some people but you cannot make them use it in the way that you think it should be used, and they aren’t going to take better care of their horses, they’re just going to spend the money on something else. Maybe a sound, fancy horse, who knows, where your money is going to go to paying for the lame one so they don’t have to, and they can just leave the animal out in the pasture because it’s only sort of their problem now.
All kinds of thought processes out there, having someone else pay while they have control over the destiny of the horse is a real win for some folks.
As I recall it, since we were kids we were always subject to the whims of the adults in our lives and so we had easy excuses for ending a riding agreement. School, parents, what have you. As an adult, I’m of the belief that you make a statement and don’t get defensive or elaborate on it.
“I’m sorry, I need to end this agreement on the 15th. For personal reasons.”
And then, and this is the hard part, you never discuss why you ended the lease with anyone. Now if the owner calls you, you might say that you agreed to pay for a sound horse, Dobbin is not sound, but then you might end up in a circular argument about “what is sound”, which circular argument has nowhere to go but bad, so “personal reasons” and then change the subject - to something like somebody is at the door or the oven timer is going off.
Then you have to put out feelers for another horse without insulting the first guy - which is why most adults use their trainer/instructor/Barn O/M to act as a go between, and get a real contract.