Brown coins don't buy airtime in their shop.

I am very very disappointed the way I used to respect this shop because it's the nearest from home and it has almost everything dispite being owned by Indians, that is not a problem to me because I am not a ******. I went to buy airtime as follows, R10 mtn, R20 Vodacom and R30 Telkom, all in all I had exactly R60 with me. I had 1 x R20, 2 x R10 notes, the rest were coins, amongst those coins I had R5, R2, R1, 50c, 20c and 10c, 10c were only making R1, and I was told the brown coins don't buy airtime, I apologized I didn't know. He didn't want to sell me but because he had already made the slip, he took away the telkom and redone for the one which had no brown ones, but because he was angry, rather annoyed he made another Mtn for 30 and yet I asked for telkom. So it means I bought mtn for R40 by force..... Can they please put up a notice that they do not accept brown coins in their shop then we can know we're not to buy with the coins as we are also hawkers. I am beginning to hesitate buying airtime from there or anything because our coins are not accepted. Very disappointed.