Moonie, HMRC opening times for phone calls have been reduced due to the lockdown and many of their staff are working from home. As a result, trying to get through to them by phone is near impossible.
It's just trying to get a client's tax code for the current tax year amended. A client could do this via their personal tax account online but this client would be petrified of setting up one and using it. Agents like myself are not permitted to access clients' personal tax accounts, they can only use their agent's log in to look at clients tax position but that system doesn't cater for agents changing clients tax codes, just looking at them. There is an online system for agents to change clients tax codes but it requres the agent to provide full details of expected employment, pension income and all other income for the current tax year so takes considerably more work than just writing a letter.