You want r/AskSpain
Rental law in Spain says that once you live somewhere for 6 months you can break the lease, but before that you’re at the whim of the landlord and whatever penalty they have for a broken lease. The law now also limits deposits to one month’s rent. It sounds like you signed a lease written to take advantage of foreigners who don’t know any better. You could speak to a lawyer (ask for recs in a Spanish sub) but not sure what can really be done now.
Does your US bank not offer online check deposits? Through my US bank app I can simply scan the front and back of a check and deposit it. I can also mail the check to my bank and deposit it that way. If your bank doesn’t offer this you should consider opening an account with one that does, because this is a very convenient option to have. I bank with Ally back home and online check deposit has been a lifesaver.