31 days turned to 5 days to data expiring

I've purchased R500 worth of airtime, and I buy this every month, but when I exchange it for data, it state that when you buy 5gig is for 31 day and 5gig night surf is also 31 days but after purchasing it it say it's expiring 01/02/2022 and I ve bought this on the 27th of the first month