Baddest service ever

Hi, I was sent by my aunt to pay her Hollard Policy at Pep store in Naledi. I gave the cashier R300 the policy is R243.80 so instead of getting R56.20 change I got R6.20 I didn't notice until I got home that I was given a wrong amount. I went back to tell them but the guy just screemed at me telling me that I gave him R250, I asked tht they should check on the footage coz they've got cameras I was told that it won't show they need to ask for it I don't know where and the manager told the cashier guy to count his till money to check if it balances but it was short with R119 already now she took him to their office they came back saying it balances they have checked on the system. There arrive a G4S car they told me that they will call me, till today I'm still waiting it's been 3weeks now waiting, the service I got was not pleasing at all and the way this matter was handled I'm not happy at all because if I had stole something from the store I would be attending a court by now getting my name blacklisted but my issue is not taken serious. Please help me I'm so angry I still shop in Pep stores but now I have to take a taxi to get to Pep while there's a Pep store around my neighborhood. I wanna sue the store, when I ask for regional manager's office number to the other store they said their offices r closed due to Covid 19 they can't give me the regional cell no. I understood and went home. Kindly pls help