The way to treat customers

Visited shop to get internet sim and data I was told to buy sim from another supplier because the manager is absent, did that. On returning I was informed sim is wrong and that I didn't ask for the correct sim in the first place. She then said that they were offline when I got agrivated she informed me she is doing me a favour to assist me. She doesn't have to help me if she didn't want to. I can take my bussiness elswhere. She then grabbed my papers out of my hands wanting to to assist at which stage she informed me that I'm not important and she doesn't need to assist me. Really.