Order not delivered

I have placed an order for a calculator which is R750 I have made a payment as the money shows it’s out from my bank as I check my statement.I have then received a email that my order will be delivered in the 27May as payment has been received. On the 26 I received a email stating that I need to make payment or my order will be cancelled. I really need the calculator that I paid for which has not been delivered as it’s exam times.It’s really disappointing to be paying for something then delivery does not happen.