Tax code changed mid-year, £340 a month gone, 51 minutes on hold

Posting the practical parts, because the emotional parts are fairly obvious.

The code changed because of an estimated figure for a second job that I no longer have. Nothing flagged it and nobody checked, it simply applied and the money stopped arriving.

The online personal tax account let me remove the ceased employment myself, and that fixed roughly half of it, so it is worth trying before you phone. What it would not let me touch was the underpayment they had already started collecting, which is what the call was about.

On timing, the best result I had was around 08:05. At 11:00 I was cut off twice without getting through to anyone.

Keep a log of every call attempt with the date, the time and how long you held. If you end up making a formal complaint, or arguing a reasonable excuse for a missed deadline, that log is the evidence that you tried.