Lidl complaint: Rude cashier and aggressive behaviour

I was loading the conveyor belt with my food items. The cashier (an Asian man) just began to pile my food on top of each other. I asked him to give me a second to finish putting everything on the belt so that I could come round with my trolley. He was very rude, began to say I have my rights – I can do what I like, I don’t have to wait for you’. He was extremely rude and obnoxious. His friend (a tall black man) also joined him in verbally attacking me. They began to mock me and laugh out in front of everyone saying that I should just go and this is the way things are done here (this is the speed they have to work at). They were both laughing at me and I also have a witness my niece who happened to be behind me in the que. She witnessed everything (and she is happy to give you a statement). The Asian man just continued to argue with me, made rude comments and went on about how he knows what he can do with customers.
I was so upset and I told my niece in a different language that I will complain about this. I am the customer and I was treated with disrespect.
I went to Lidl a few times to find the Asian man but he was not in the store.
I did go into Lidle today (Wednesday 3 June 2020 and he was serving. I purposely did not use that lane because I did not want to be served by an aggressive rude cashier. I asked for his name. He quickly covered his badge with his hands and removed his name badge and hid it from me! His manager called Jazz approached me and told me that he will deal with it. He was a professional, kind and quite empathetic. He told me that he could not give me the name of the cashier (this is against the law and I will be seeking advice from a solicitor). Jazz would not give me the cashire’s name – I asked for it because I wanted to formally complain. Jazz obviously did not want this Asian man to get into trouble.
Jazz also told me the name of the cashier is on the receipts. I told him that this incident was a few weeks ago and that I had not kept my receipt.
I would like to put a formal complaint against this individual with immediate effect.