Bolt driver doesn't want to give my change back

I would like to condemn the conduct of the last driver who gave me a ride Rofhiwa. The trip took place of Friday the 9th of August 2019.

The guy didn't have change on him (the trip costed R74 and he only had R6) and we agreed to buy me airtime using the remaining change R20.

I have reminded him to honour the agreement several times and he keeps promising to send the airtime.

I really need my change the same way he needed the fare for the trip. If my money had been short by R20 he wouldn't have offered me a ride but he sees this as normal to keep my change.