Renting a home and are responsible for utilities, lawn care, basic repairs, water, landlord picks up mail at home.

We signed a lease Oct. '13. Our lease has gone into the month to month stages. The lease had an agreed upon rent of $900 per month and we have since worked out a $750 per month agreement. We have been nothing but upfront with our landlord and she seems OK with what we've told her. We get letters from her non-legal representative and we get another story. Since agreeing on a rent of $750/month, my father died and we lost most of our income. We've tried working with our landlord, she takes it up with the 3rd party and we don't get a voice. They are now wanting almost $7000 in back rent from the original $900 agreement. The landlord still picks mail up at our house and we are responsible for all upkeep, utilities, water and conditioning, lawn care. What are our rights as tenants?