Voting cards weren't send out. You got a booklet instead detailing the constitutional changes with a cut-out portion on the back cover with your details that you can use in lieu of a voting card.
Be aware that the online voter register isn't 100% accurate. I'm not on the online register, but I did get a voting card/booklet! This has been the situation for a few years, since I moved to my current address. The Co Council can't explain why I don't turn up on the online list but am on the paper list!