Just send them the written notice of termination of tenancy.

A fixed term must be explicit and give an exact beginning and end date. If they don't have that in writing, you probably just had the normal annual lease that transforms into a monthly automatically renewing lease at the end of the year.

If they wish to be jerks, you can see a lawyer or paralegal. There are several tricks to making them agree that a pro can walk you through.

One of the easiest is to offer to assign your lease to someone else. That means someone else takes over your lease per the terms of your tenancy agreement, and the landlords don't get to raise rent for the new tenants. Most landlords will balk at this, because they usually can make more money from a new tenant, and they have less control in this process.

But that's probably not necessary. If they want to enforce a three year lease, its up to them to prove it. Unless you signed a tenancy agreement for three years, you're in the clear.