Reoccuring Incorrect Simple Assessment

I resolved an incorrect Simple Assessment years ago with the customer support over the phone. They said everything was sorted. Then a couple of years later I get the same Simple Assessment calculation saying I haven't paid. So I rang again and they said it was a mistake and it's all sorted. Now, a few years later, i've just recieved the same Simple Assessment again. This time I have tried to call the customer support line countless times over the last month but it is always 'very busy' and they can't take my call and the phone line hangs up. (0300 322 7835) How am I supposed to resolve this if the only communication method won't let me even get into a queue? Is there an email address I can contact, can someone arrange a call back?

Hi Richard Fox,

If you are receiving a Simple Assessment calculation you can discuss this with our Income Tax department:_
Income Tax: general enquiries

Thank you.