Complain about store assistant and the store manager

I bought a cell phone which they said I must return in 7 days if I'm not happy about it. Phone is mobicell. I went back to them on the 16-01-22 having bought it on the 14-01-22 because it freezes and the battery life is not good. Now they say I must stand on the side until it starts freezing while thayre helping other people. Sales person Siyanda and store manager were very rude, store manger even threatened physical harm, she said she'll some men who'll harm my boyfriend. They are telling things that are not on the agreement document. Andiswa the manager said its common sense that I shouldn't erase everything on my phone when I'm taking it back, they are not trained to work on cell phones but they say the information they have is enough for them to check and reject whatever complaint if they feel like it. I have never seen a manager of the store swearing at a customer even worse threatening one. Please look into this for me