New duplex, inherited tenant problem

[Dean Klein]

I just closed on a duplex and inherited some tenants. The current leases are written in such a way that they lock rent price in for a year period, however there is a termination clause of 45 days to non-renew the lease. The rents are way under market so I decided to send non-renewal letters with almost 60 days notice and offer a lease of my own explaining the current rental market conditions, and current going-rate prices. I heard from the previous owner who I bought the property from, that one tenant is livid about the rental increase, and is going to turn me in to some rental board, not sure what that is. This tenant went to the previous owner to complain because he rents a commercial spot as well from him. This tenant only has about 6 months left of the original lease. I have never seen a lease that locks in a rent price for a year, but has a termination clause with a set amount of days notice, anybody else deal with this? I believe this tenant is going to be difficult to deal with. 

EDIT: Property is in Wisconsin.