Won’t refund me for a credit balance or respond to my emails

Over two weeks ago, I received a receipt from Ampath indicating that I had been overcha for a blood test I had taken. I called their customer service and was informed to fill in my banking details and wait 7 days. I did as asked however I received no feedback and after 7 days I emailed them again but didn’t receive any responses. It’s almost been 2 weeks now!!