Error?
"The Electoral Commission said it is working on identifying how many EU citizens have wrongly been issued polling cards allowing them to vote"
They didn't say or shouldn't have said that. The polling card does not allow you to vote. I'd say it invites you to vote, but, as explained, you may be not entitled to, and the card doesn't prove that you can.
Maybe you could apply for quick British citizenship if you do want the right to vote, but that isn't easy to get if you don't have it, unless you are rich.