Lockets that is horrible feeling like you have been told off by them on behalf of everyone else when you barely did anything...compared to come who really did abuse it.
I didn't think of it as a glitch - these things are often totally bona fide - and I don't therefore think it was dishonest.
I don't think you need feel bad. Plus if it helps Littlewoods and Additions are notorious for getting things very wrong - I have had it go both ways, they've sent me a statement with the discount applied twice, then another identical statement sayingthe first one was wrong but I had already picked up on it and rung them to say they'd undercharged me, and they agreed to take the payment, all very well - on another occasion I was sent four sheets instead of two (bear in mind I have on average had about one order from them every two years, and still!!!) and told me to keep the extra sheets which was kind - but they have delivered things which were just AWFUL quality and messed about with deliveries and days, not adjusted accounts, and once I bought insurance for a product which they then failed to cancel despite about 5 phone calls asking them to and I kelt the certificate for 3 years as I never quite believed they had finally cancelled it - turned out they hadn't, and I claimed on it in the end but that again took them weeks.
They are such a disaster in terms of admin that they surely have no real idea who owes them anything or whom they owe...it's ridiculous. Plus their prices are a con from the off.
And I am almost sure that this little charade will have been deliberate, because they have done it before and once they see how many people sign up and order, they can look at their profits or losses and decide where exactly to place the minimum (ie £50) and then tell everyone in retrospect that they should have spent £50. It's really really naughty.
Please don't beat yourself up - I know, I would be too, but it might easily NOT have been a glitch. And I don't think you were dishonest because you rang them to check.