Are you on a EE Subscription Pack, as you will most likely just need to use that £20 credit, or some of it, to buy more data yourself.
It won't automatically add more data for you if you've used all the current subscriptions monthly allowance, all you have done is topped up your credit on the phone and you need to use that yourself to purchase more data.
See this similar post here as easier than copying parts from my post there!
£15 sim bought online but £15 not credited to phone number
If you are still having issues, then it's best to contact EE themselves.
https://ee.co.uk/contact-ee
Also, note you don't get refunds if you're on PAYG, see here....
Want to get refund
Subscription Pack Refund
I do not subscribe, so please do not always expect a reply.
