Bad Cutomer Experience

I would like to formally log a complaint over the level of service I got from your Mall of the North(Polokwane) branch. I was in the shop on the 23rd and bought make up, yesterday returned to the shop after I realized that I got the wrong color. I did not have the slip as threw it away, was advised there was no manager and she/he was off for the day and they can only assist today. I explained to them that I used my ID number for rewards, they can track it, even showed them my bank statement on the phone reflecting the transaction, was advised I must come back today as the manager will be available. I explained that I’ll send my husband as I’m in a meeting for the day. I went and digged in my trash bin for the slip, as they indicated that the reason that they are not changing it yesterday was because I don’t have a slip. My husband just left your store now and they are saying the manager is still not in and they are accusing me of opening the make up. Why would I go to this extreme length of driving 30km to mall and back to my house yesterday and today if I had opened the make up. I was there yesterday and showed them the box, they did not even bother to open and check the contents and only today they are claiming that its opened. Why would I take something back if its opened. Why would they waste my time and travelling money if they had no intention whatsoever. Why would they say manager is not in yesterday and assured us that she/he will be back today and there is no manager. All I need is to swap to the correct color. Do we really have to be treated this way