refund?

hi all i purchased an ipad pro for my son ,3 or 4 years ago which he has looked after ( in a solid rubber case) recently had battery issues with it,up until then worked fine, i phoned a tech team who said it was no longer under warranty but if i sent off 100 quid it would be repaired ( battery's replaced) , now they say its got other issues and will be 400 quid?? What ??? ,i have asked them to send it back,which they are currently doing,but what about the 100 quid that has already been taken from my account?