Has my usage allowance changed?

[#1]

Has my usage allowance changed?
Have I been moved to a different package because I'm having connection problems?
Just got an email saying I was approaching my limit for the month.  I thought I was on ‘Option 3’ which gives me an allowance of 30GB per month.  I’m nowhere near that.  Is the email an error?  I don't understand.  Can someone explain?

[#2]

Have you reached 24GB during peak (paid for) time, I think you get an advisory email when you get to 80% of your monthly allowance (or is it 90%)?

[#3]

Right first time - 80% 

[#4]

Hi there,
Your usage allowance hasn't changed, the email sent was a warning email as you've just hit 80% of your usage allowance.