Nasty letter telling me I had not paid a bill

I was a LOYAL customer of this company for more than two decades. I always paid for my shipments ON time or earlier. They sent me a nasty letter telling me I had not paid a bill and threatened me with collection.

I sent them every check number, w/ amount sent to them and the dates. I had a shipment enroute to my home as this was transpiring. I REFUSED IT. I have not even been acknowledged. NOT ONE word from them regarding this issue has come to me. I refuse to spend another dollar until they apologize.

This is NOT how you treat LOYAL customers. This is how you LOSE them.