When we switched our utility to DH company we had to sign a contract that said that if our account went into collections he would be terminated. Did you ever sign something like that?
Definitely consult a lawyer. Before he has to go to HR if possible. Since he works there it seems like it would be easy for him to explain his way out of it. The first incident wasn't his/your fault. And I'm not convinced the second incident was his/your fault either. Were you getting late notices for the second incident or just the cut-off notice at the end?
Hugs to you! I feel for you and hope this all works out right and fairly!
I'm sorry that you are going through this. I think it would be in your best interest to get a lawyer to help you. It seems to me that the company is out of line, but an attorney could guide you. Best of luck to you.