How long is a week?

Good day <br> <br> I joined planet fitness about 3 weeks ago. I received 3 vouchers for friends or family to use the gym for a week. My cousin used it and on the 5th day they tell him it's only valid for 5 days. But it says clearly on the voucher a week. Apparently According to them a week is 5 days. I think this is false advertising as no where did they say 5 working days.