Property Manager Collecting Wrong Rental Amount

[Nancy P.]

We raised the rent from $1250 to $1300 last July 1 on a property we own.  Tenant has been there for 4 years,  he's always paid a bit less than tenants in identical property because he moved in November,  at the time we had no other qualified applicants.  Should have stayed vacant as 4 years at $100 or more below market value has equaled more than three months rent. (We would have gotten a market rent tenant in January or February.  Relative Newbie error,  we've only been doing this since 2010.)

Current lease ends 6/30.  We moved to Germany for a job in early June last year,  he signed the lease before we left.  We hired a PM to manage our 7 properties.

Turns out our tenant has continued to send $1250 a month to our PM,  who never looked hard enough at the lease to catch the mistake.  (My mistake too,  for not catching it until now.)  He just saw my spreadsheets that said $1250.  Now,  based on my experience with this tenant,  he could be just stupid or trying to pull one over on my PM.  Either is possible.

So we were finally catching up to market rent this year at $1350.  Tenant says he won't renew at that price,  that $100 is too much of a jump.  THIS is where I catch the mistake as it is really only a $50 jump from rent stated on the lease.  

Tenant and I are emailing directly at this point.  He says he "didn't know"  rent was $1300.  I have emails to the contrary.  He complained about the increase but accepted it.

He says fine, he's not renewing,  and he's not going to pay the $50 x 10 months he owes (12 by the time he leaves).  He says since we accepted the rent for ten months without comment,  he has no obligation to pay it now.  Also,  that he will sue me if I take it out of his deposit when he leaves.

My reading of the lease says otherwise,  but I think I'm better off just letting this guy go (he's a PITA anyway) and eating the $600.  My husband is adamant that the tenant pay NOW or get evicted.

Has anyone had similar situation for whatever reason and how did you handle it?

Thanks.