Inconsistent Payment Grace Period on Packages

I recently upgraded to Compact package from Family, thus prior to upgrading Family package,I was advised that there's a 48 hours payment grace period (Family package). I made payment of R300 on 03 December (07h27am) however,I was penalised R50(allegedly for late payment). My concern is by the time I made the payment it was not even 36 hrs. I need to be educated on how the payment grace period works and applicable on which packages. Moreover,if such important information may be emailed to me so I may have something to refer to.