Threating e-mails

This is the most irritating company I have come to deal with. I have been paying them every month and have all the proof thereof, I have been trying to get a hold of the company but no one ever answers the telephone, nor the e-mails I send.

Now I have been getting threats from the company about a summons and blacklisting me.

I connot work with people whom do not contact you back nor identify that you have been paying.