Doctors asking for payment of the bill for the incomplete treatement

So my doctor agreed to treat me as a favor to our mutual friend and he did. They never gave me the bill. And because of this they didn't do the followup treatment and that led to worse consequences and I got treated by other doctors. But after a few days he started asking for money and wouldn't take no for an answer. It's been 9 months now and they have been harassing me in so many different ways. They are threatening to go to police. Am I liable to pay? Considering they never legally billed me. Can I go to consumer court with this? Their collection agent came to me when I was in a meeting with my client and the way he spoke lost me a client that could've meant lakhs of money. This is mental torture.