Bill me for services not done...

We had a little credit with Servest Hygiene until about August last year. I then received a statement from them saying that they had carried out a service and I owed them money. Firstly nobody came here to do any service, it took months to query to no avail. I then requested that they credited me and refunded the credit we had back to us and I have not heard a word since... There service and attitude is disgusting, I cannot believe that they are so successful when their service is so terrible. I will Never us any Servest service again in my life!