Conned to give ID

I chose 2 track pants, 2 tshirts, and a sweat-shirt, then stood at till for 5 min, when asked if I should come back later I was helped. I was told unless I gave my ID and cell number I would not qualify for the discount. I asked the person behind the counter to show me where it said that and low and behold in very tiny print, it said at the bottom of a poster in very tiny writing you only get the discount if you a club card member. The staff got so agresive with me I had to basically exit the store swiftly, to avoid confrontation. They were so smug that they could point out the fine print, not even realising they had lost a customer. Every person I speak to will hear this story and I will never go back. I don't shop at stores that ask for my ID number sorry.