Best answer by terrywebbs
From memory I think you will find this is correct, your current upgraded allowance is calculated on pro-rata basis until the next full month, so it's only showing part of the allowances.
Has something to do with timing, if you upgraded exactly on your anniversary date of joining it would have shown different again, more in line with what you expected it to show.
Next month it will work itself out, I am sure!
How will my current month's cost and allowances be worked out when I change plan?
Until your next bill is produced, your current month's plan cost and allowances are worked out as follows:
Plan cost - The pro-rated totals from your old and new plans. You pay your line rental in advance, so you'll get a credit in your next bill for the extra line rental you've paid.
Allowances - The total allowances from your old plan, plus the pro-rated total from your new plan.
The fact that we don't pro-rate your old allowances is good news, because it means there's a good chance you'll end up with a few extra allowances until your next billing period starts.