(Only applicable if you have taken out a contract since Oct 1st 2018)
You can now choose to apply a Spend Cap with your monthly tariff, to help control your spend on out-of-bundle charges. Any chargeable usage outside your monthly allowance or outside of any Bolt On allowance will count towards your Spend Cap.
Charge to Mobile is a way of buying digital content. If you are Pay Monthly the charge will go on your bill. If Pay As You Go, the money will be taken out of your credit.
If you want to avoid these charges completely, you need to call Customer services and ask them to apply a bar to CHARGE TO MOBILE. Just remember if you do want to use the service in future you will have to ask for the bar to be lifted.
Many people find themselves inadvertantly signed up to a payforit scam. These sites are numerous and people will find themselves incurring a monthly charge for something they neither want or need.
The most common reason for this happening is when you click on a link on FB or other social media site and are redirected to another payforit site. (The forum already has a guide giving a full explanation about these sort of scams. It will be linked to below)
To avoid this happening, do NOT click on links if you are unsure as to where they will take you.
As an added safety precaution, ask customer services to place a DIRECT TO ALL BILL DEBITS BAR on your account. This will ensure no money is taken from your account.
If you are unlucky enough to find yourself a victim of one of these scams, then please take a look at this community guide and website which gives information on what to do next.
EDIT: From 11th May 2019, O2 and partners have introduced a 2 step verification process to avoid customers signing up inadvertently to these scams. Also, this will include a pin sent to your device or a text, which you will need to respond to before any payment is taken.