Day light *******

I purchased data for the following number *** on the 27/05/2020 2G 30 days for a R140. On the 30/05/2020 I received a message from Telkom that my data is expiring the 31/05/2020. The data did indeed expire the 31/05 2020. i would just like to confirm how 30 days is calculated at Telkom. Could i please be reimbursed my data that was taken away in three days which was supposed to last 30 days. i have a contract with Telkom and have never compalined about anything even though most of the time the network is terrible. Robbing me of data that i bought is taking it to far.