Recently Purchased home - Tenant claims rent is wrong

[James Godbout]

Hello,

We closed on a house yesterday, a rent stabilized (or so we thought) 3 family. One of the units was currently rented for $3300, with an accompanying lease and last month's rent deposit collected at close. However, the tenant is now claiming his actual rent was $2800, and that he did not sign the lease that we have on hand. Has anyone ever dealt with a situation like this? any advice for me on how to aproach this issue?