Lidl complaint: Accused of stealing

I have now lived near the Lidl on Kirchenstrasse for 3 years. As an American, it is appalling at how rude the people who work at the cash register are (with few exceptions). Today I was told (not asked) to show my backpack by the woman at the register, in a very rude manner. I had walked from a nearby Indian store next to an Edeka (I shopped at both stores) and was on my way home when I realized I forgot Spezi. Not knowing that I have to announce my groceries (which is logical and I do not disagree with), I walked into Lidl. Therefore there were groceries in my backpack, but clearly nothing that is sold at Lidl (some items even had the Edeka label). She then said somethings might be sold at Lidl (which I have shopped for three years and know they are not sold there) and then got angry when I said No you do not sell this here. The only thing in my bag that might have been from Edeka was a zucchini. Anyways, this all leads to the following: customer service at Lidl is horrible. The cashier could have nicely asked me next time to leave my bag at the front but instead was accusing me of stealing and being very rude. Another time, another cashier yelled at me when I said I didn’t want one (!) tomato that clearly had mold on it. It’s incredible that these people are still allowed to work there.