Tenant(bank ) lease expired and not paying market value rent
Bank Lease got expired in sep. 2015. Then my father(land lord) started giving bank letters saying that he is interested in renewing the lease and also talked in person to them and bank said they will renew the lease verbally but never commit. after several ways of communication my father gave them legal notice in march 2016 to either renew the lease or pay X amount until bank leaves. then bank agreed to renew the lease and gave a written letter of proof for it and my father needed to to some changes in the property. he did those changes and communicated that to bank. in the mean time they asked my father to cancel the notice and he did. but they again stopped responding even after trying certain mode of communication and started stalling. after getting fed up my father gave them notice again aug 2016 to pay agreed rent since lease expired and keep paying until bank stays. then bank responded that they will not be renewing the lease and will not pay any increment in rent. what are our options here? even after giving sanction letter they are backing out. without paying any increased rent.