Poor pep Customer service

I was @ pep cell park station to pay my vumatel account and ask the cashier to give me R200 change, she gave me 2 R100 notes of which 1 was ****, I noticed it when I want to pay at the certain supermarket when it was rejected. Now I have been sending emails and make calls to their customer care and it's been 4 weeks now no respond. Pep cashier in park station knows very well and I think they robbing customers, when I went back they refuse to change it for me.