Is this normal for an accountant and HMRC to be constantly so far apart?

[Loulouboho]

Two years in a row I pay an accountant to help me with my tax return and honestly my confidence in her is very wonky at this point.

Last tax return she told me I might have to pay ~£500-600 and then I got hit with a £9K demand. This year she told me I was due a >£5K tax rebate. They have offered me £250.

Why is this so different? I literally struggling to understand how to fill this and calculate it which is why I pay her to help me. I feel as though my confidence is just gone now in this accountant. Is this normal to get it so wrong?

I don’t understand how there can be a difference if she’s submitting the return? She’s literally inputting the figures onto the system. She has a tax figure that she tells you to pay but when you log into gateway the amount is different?? When you approved the return which figure was on it? The one she told you or the one showing on gateway?
I suspect it’s the payments on account that maybe haven’t been explained properly.