My dad's friend used to own a building and he asked my dad to rent a space. No contract signed everything was oral. My dad stayed at the building and ran his business and paid his friend/owner a monthly rent of $5000. After 4 years, the owner said he needed to sell the building so my dad needed to retroactively sign the lease. He said it's only formalities, and that he spoke with the new owner and that the new owner would not raise rent. Without reading the contract (my dad can't speak english), he signed the contract. The new owner comes in and says the rent has been increased to $6500 according to the contract. My dad has been paying $6500 until now but he wants to get out of the contract. What can he do? Can he just give notice and leave the building? Is the contract valid?