@JPJ2001 You’ve joined the EE community as you’ve posted on here.
If you’re trying to purchase an item from the add to plan store and you’re not already a EE contract customer you can’t. The add to plan store is a perk of being an EE contract customer and you spread the cost of the item over 11 months when you are billed for your EE contract.
To contact EE Customer Services dial 150 From your EE mobile or 0800 956 6000 from any other phone.
