Banking example: trying to move some savings from one UK bank to another - back to where the money had originally come from, and that had just purchased the first bank too. It took 8h on the phone over a week or so to get the money back, which was interspersed with a comedic number of calls from withheld numbers and people unknown to me demanding enough info to get access to my money. And other very poor practice. The bank even conceeded at least once in writing that it knew that it was screwing up and sent me £100 by way of apology - but carried right on screwing up.

Non-banking: getting a call out of the blue from my Internet Service Provider again demanding enough credentials to get access to my (business) account, and unable to understand why that was very poor practice. I used to like that ISP a lot, and have been with it for a looooooong time, but the angry exchange with who seems to have been my account manager has soured the relationship a lot.