Self-extending leases are legal. The standard ones (if that's what you have) require that either side notify the other if the lease is not being renewed by a certain number of months prior to the expiration. In your case it was one month. It sounds as though your lease auto-renewed with all of its terms intact. I have not seen the lease, but based on what you have written it is my opinion that once the lease self-renewed neither side could change the terms, and a rent increase is a change in terms. If the landlord gives you a hard time you might think of talking to an attorney.
Ellen G. Friedman, Keller Williams Realty, email@example.com