Rude supervisor

Standing at pick n pay and I requested klim,the supervisor a while ago gave me a range check however upon arrival he tells me it is invalid claiming I must pay the difference as he can't do anything about it anymore.one of his employees comes and says they only give it to selective customers. What makes the next a selective customer??? He then starts argueing with me and screaming to which I retaliated back and scream at him. He was not listening to me as I was speaking and just argueing! Is this how pick n pay trains thier employees to treat customers??to make it worse he is a so called supervisor,so how do people take an example from him as a leader??does pick n pay teach employees to scream and argue at pick n pay??very poor service as a well known company please train your employees how to treat customers