Oh, what a nasty experience, OP. Hope you're feeling better now. Reminds me of years ago, when I bought a very nice bag in Sogo, the Japanese store near Piccadilly Circus (now long gone).
The assistant opened it, removed a security whatsit inside, then carefull wrapped it for me. As I walked out, the alarm went, and a huge security man GRABBED me by the arm and hauled me back into the store ... as I was turnng to go back in anyway! I showed him, and the assistant, the receipt just issued to me. The bag was undone and ... in the bottom, underneath the balled up tissue paper inside the bag, was another security tag! Assistant was mortified, security man didn't seem to care and I was bloody livid.
At home, I fired off a fax to the store, followed with a telephone call. Within half an hour, a courier arrived with the huge box of chocolates from Sogo! But I felt shaky for ages after and never went in there again.
As for Boots, some items (mainly cosmetics) have to be scanned to 'de-security' tag them, and three times now assistant has forgotten to do that. I always walk straight back in and show item, receipt, and make them scan it again. I complained after second time to Boots head office, but it still happens.