Am I obliged to continue payments to a company for reducing weight if they caused harm to me?

I applied for fat-freezing to reduce weight with one company. They said they would give sessions for 4 months. I made all the documents and signed a consent form, and they made an EMI from Tabby for 4 installments.

I made one installment and took only 3 sessions. But their services are not good and they gave me scars and red bruises near my stomach and love handle side.

I didn't continue the session further and I told them to cancel my further session and the other 3 installments to reverse them so I don't need to pay when I am not using their services further.

They are not canceling my installment and saying I need to continue the session and make payment.

What can I do as an option?

They are not reversing my other installments for the service which I didn't use. They are still saying I need to pay despite all the scars I showed them near my belly side scars because of their fat freezing.

They promised me it would be painless, I got scars and bruises but they are not willing to reverse and cancel my other 3 EMI installments.

Please guide.