OK guys, I found the issue. For old accounts, repledging doesn't work, but UPGRADING does!
Remember, this is only for people who have pledged but have NOT been billed already!
Go to Your Pledges (https://www.patreon.com/pledges), click edit pledge, then change your pledge amount to be double what it currently is. You will be billed for the difference. After being billed, change it back to the normal pledge amount. Presto! All done!
For example, if you originally pledged $20 (but were not billed), go change it to $40. You will be charged the difference ($20), then edit it and change it back to $20. Easy! I tested it out on deathblade's Patreon right now and it works!