Customer robbing us our change

On the 17th of January 2021, I sent my 12 year son with R20 to go buy vinegar and soup, whereby he paid for 2 packets of soup only giving them R20, on the receipt the consultant by the name of shandies only rang R9, 58 as cash and as total, whereelse he was given R20 but only gave my son 40cents as change, I went back to the store as his parent to get them to rectify the mistake they made, I was told that my son gave them R10, the manager also went to her office to view the footage alone, not allowing me to see the proof of what happened with my transaction, then she came back from the office, saying she only sees my son giving them R10, my other concern is they are also selling expired and rotten stock, then so not even check their stock as well, the lasy who is the manager in the store is very rude towards the customers, I'm very unhappy with the service that I had. This incident happened at Usave zone3 Seshego No 52 kwena Moloto.