Longstanding issues with work over pay. They owed me £500 from miscalculated pay and it turns out I've been paid back the correction twice.
For back story, employer was horrible. utterly fastidious, and expected (and generally got) 100% accuracy from employees, yet made mistakes every single month with pay/holiday etc. I stopped mentioning their mistakes after the first couple of times because they so shitty about it and it was only because I was leaving that I dared to mention the £500 (a new, totally different payroll issue to the ones I spotted every month).
I got let go in a horrible way so definately clouding my judgement as to whether I should tell them about their lastest error or just put it somewhere safe until they notice.