Not sure what you mean about 'metered option'? If you want pay-as-you-go then I guess you'll need to change your contract.
Clicking http://add-on.ee.co.uk/status will show up how much you've used, if you've used up your GBs you'll be given an option to purchase more.
For backup we've got GBs on the mobile phone, if my laptop is using the mobile GBs the same link above will show mobile usage status.
Some people have their camera, laptop configured to send the image/data to icloud for storage. Therefore your quota can soon run out, especially if you like snapping pics a lot.
Thank you Rich for the tip, brilliant, when we get back to Nuneaton we'll call into the EE shop. Think our dongle is faulty, it's not recharging like it should, we've tried different usbs on laptops, tablets, and via a usb/3-pin without great success. Strangely when we got the dongle it didn't have a charger with it.
The huge Win-10 upgrade could have been the problem. It was pain in other ways too as I had to re enter serial numbers of purchased software (yes, I know I should keep these details in a safe place)!
Thanks all for helping