Doctor Rips of medical aid

In July last year my wife had a minor procedure done at Parklands Hospital and the presiding doctor requested Dr Y Vatharajh as anaesthetist. I later received an invoice for R13888.00 from Dr Y Vatharajh of which my medical aid covered R12189.24 as per medical rates. In October my wife had to go in again so I approached the presiding doctor with the issue at hand and asked him to get another anaesthetist. He said he will speak to her(Dr Y Vatharajh), not to charge over medical rates and ask her to waiver the outstanding balance from the previous statement. After the second procedure I then receive a statement from medical aid for a request of R13087.00 (all this for 5 min of work) of which the medical aid paid R2138.78 which was medical rates. the balance of gap cover (R8551.00) was paid into my account in 31/01/15. In the meantime the doctor, without consulting me first, has handed me over to a collection agency and is demanding over and above what the medical aid paid into my account plus their cost. Total rip off. Please don't use this ANAESTHTIST