AIBU to be pissed off in the supermarket queue has a go at me for being rude to the shop assistant, when I had a valid reason

[CarpetDiem]

So, I was stood at the check out, woman in front was packing up her stuff, I was getting served. The girl on the checkout had already put her 'till closed' sign up behind my shopping. A woman in her seventies came up & tried to put her shopping on to be told 'I'm closing now' fair enough, two minutes later a twenty something couple came and did the same & she said nothing. So I said 'sorry she's closing now' & the checkout girl said 'it's ok' I replied 'er, no, that's not fair, you just sent that older woman away' she huffed & repeated 'it's ok just once'. I was not amused, I hate unfairness, especially when it was blatantly ageist. So when she asked me if I wanted a bag, do you have a points card? I said 'no & no' to which the customer in front of me ( still packing her shopping) said 'there is no need for you to be rude to her'! I said 'what's it got to do with you?' & she repeated herself, as did I. She walked off gossiping away to who I presume was her mum.
AIBU? I've just got home & it's really pissed me off

[Witchend]

I agree jelly and Worra

In fact I wrote to Next last year and told them so, and requested that anyone who had been involved in making that decision was attending the busiest store.