I would feed him what he is used to for to the first few feedings then try to switch over to F/T. It can take a bit of work to switch them over. Also wait a week between feeding attempts as offering too often can cause stress and make them not eat. A stressed ball python will starve itself. You really should have given him a week before trying the breeder gave you bad advice. Just make sure your husbandry is on point. Feel free to share your set up and temps so we can give any advice to help you be successful. Also no handling till he has a few meals in with you as that is stressful also.