How to buy Extra GB's?

[#1]

Product = PlusNet Broadband Your Way Option 1 (Monthly Contract) with included 4GB bandwidth.
Quick question - Is it still actually possible to buy an extra 1GB in advance - cost 75p - as opposed to choosing the automatic £1/GB option, or actually changing products to include 5GB?
I know I've done this a few months ago, but the options appear to have changed, & following the instructions in the "How Broadband Your Way Works FAQ" actually now seems to lead to changing products - not just buying an extra 1GB for that particular month.
Apologies if I've missed something!

[#2]

If you want pre-pay bandwidth at the cheaper price then it's always involved changing the base-line product AFAIK. This was how it worked on the legacy PAYG products too.
If you go over your allowance and are on the 'flex' option then extra GB's are added for that month only but at an additional cost.

[#3]

Thanks for quick reply - I must have remembered buying an extra GB wrongly