Billing Problem

I cancelled my rain sim on the 1st September 2020, as I moved back to my University residence, I got the email saying it was cancelled. And as soon as it was "cancelled" i stopped using it immediately as I didn't need the data anymore.

According to Rain's website it states: "The cancellation will take place on the last day of the month, but you will only have to pay for the data you've used."

So I understood that they would charge me for that day, which was fine. but then today I saw that they deducted the full price. And as a student that did not use the data that is not fair, I tried calling but was never answered, I eventually ran out of airtime. I then emailed their customer service which was of no help.

What should I do as I really need my money back.