This would really suck if you were put onto emergency tax, which temporarily takes away your tax free allowance.
The government would temporarily take £209.50 a month extra while the useless chat bot would be unable to help. After 6 months you'd be short by £1,257 which, for some, would be devastating.
The lack of a helpline doesn't make any difference, if you get put on an emergency tax code it'll stay there until the end of the tax year anyway. This usually only happens if your new employer is shit or your previous employer was shit and/or stealing your taxes.
Not defending this, mind. Underfunding tax collection and making it really hard for people without expensive accountants is ... exactly what we have come to expect of the robber barons who run the country.
Ah, maybe one of my experiences isn't common. Mine started after a benefit was added and somehow not reported, which probably was my employer's fault but I didn't get anywhere with them. Reporting it seemed to clear it up.
I have had it where a second employer totally messed up which just involved waiting until April. Then another where a previous employer failed to produce a P45 and I just had to push them for it. Those are probably more common and, you're right, the hotline didn't help.
I've been at a small company where I've overheard directors talk about how they purposely didn't produce a P45 out of spite of someone leaving. It relies on good faith far too much and is confusing to navigate.