Utterly disgusted

Accidentally bought Cell c Airtime to the value of R150 instead of Vodaco and only realized my mistake before I even left the counter,asked the cashier if it could have been changed but she said unfortunately she can't do it as there are any refunds on Airtime,I asked for a manager and when he came the response I got was that he will come back to me,after a few minutes he came back and said that they can't refund me as they don't do that with Airtime,I mean I didn't even leave the store and I got was that they can't help me,so much from a supermarket that I have been supporting for the past 6years,to say the least I'm utterly disgusted and don't think il be setting my foot in that store ever again,I'm sure pick n pay would welcome me with both hands,sis man