I purchased a sliming programme for which first installment was done by credit card. When i went to the center?

for starting my programme i came to know from their doctor that , it is not recommeded for lactaing mother to start the programme till the time they are lactating. Then i told her when i came for consultation they told me since i am reducing lactation so i can start the programme. Now after knowing all the things i dont wish to continue with the programme . Can i stop the payment for the transaction that i made by my credit card to pay to the slim center.