MTN don’t care about it’s customer base

I completed my contract on 16 June 23 and only went into the tygervalley store on 24 June 23 to downgrade my contract to airtime and data at R229 per month instead of the R950 I was paying. They said from 1 Aug 23 I would start paying the new amount. In 1Aug they took off R929. I went in and they said it was a penalty of R600 for taking upgrade early. I only took downgrade 8 days after expiry. They say it’s a mistake but MTN keeps the money anyway they don’t pay you back even although it was a MTN mistake. They credit your account and let it come off future payments. Is this fair, maybe fair for MTN but not for the customer. MTN do not care about thier customers they have a take it or leave it attitude. Very shameful for a large corporation