When dealing with banks that I know have lousy customer service over the phone I keep recordings. "Recordings may be taken for training and customer service purposes" says the message. Thanks, I'll take your advice.

In the UK the tax-free savings account allowance is per tax year. I paid the money into a not-so-great bank offering excellent rates a few days before the deadline one year and called to create a savings account. Weeks later they've got no record of the savings account, and when I call they explain I'm too late now for "last year's" allowance. I point out that I made the transaction before the deadline and they explain that oops, sadly they don't have that call recorded, and so there's no evidence I actually authorised account creation back then. So I play back my recording, and what do you know, suddenly the bank has a new explanation for what went wrong and wants to pay me compensation for their mistake in not making the account.

A better bank would have eaten the cost of this mistake up front of course, but I already knew this was a lousy bank, that's why they're offering by far the best rates. To attract customers despite the reputation.