Incorrect vitality Debit

My gym visits are at 36 in a rolling 12 month period since February 2016 yet my account was debited with a 50% discounted amount and not 75% discounted amount. The lady at the call centre says that the information was given to them on the 12th of February yet I met my 36 visits subsequent to that date but before the end of February 2016. She said that this is how Planet fitness works yet this is in contravention of the DIscovery Vitality rules which is that you will get a 75% discount if you meet the visits.