Buying airtime

Standard bank has a ussd code where one can buy prepaid ( Airtime and electricity) without having airtime in your phone. for me that USSD gives me a technical error every time, I struggling so much as most of the time is emergency. it is very frustrating because where will I get airtime in the middle of the night when shops are closed or I am in the office and there is an emergency at home and I have to call.