Rental contract has expired, tenant refuses to renew it and tenant is owning 2 months rent?

my tenant is an organization, their rental contract has expired and they have not responded to my 60 days notice for renewal and they are owining me two months rent.
what should I do,they have no contract as of now,do I go through the legal eviction process or can I lock up my property?.
I have been to there office , the person incharge refused to see me, I have called them several times they never answer my call, I have sent them email and have mailed notices to them but no single reply or response.
what should I do at this time ?
one of their worker is living in my building. she is not my tenant directly. the organization is my tenant. she is aware that rent hasn't been paid.

First of all, there should not be a residential tenancy within a commercial property. You serve them a notice to quit. I suggest you hire a property management firm to handle your business because you don't seem to have a backbone.

I would look into the laws of where you live. If your tenants are not responding, they are relying on you to do nothing. If it is a small amount look at your local courthouse. Many have brochures on how to file. If it is large seek legal counsel. Their expenses could be won from your tenant.

When the rent is not paid for any reason, start an eviction IMMEDIATELY. Contact a real estate attorney NOW.