Contact MS here: http://www.bing.com/rewards/contact
Thanks for that site. Maybe I'm blind but I couldn't find a link anywhere on Bing.
After looking, it turns out I had redeemed four Tango cards on July 26 with all four saying "Complete."
It's bit calming knowing others are having this issue as well and it's not just me. That tells me it's happening on their end and not mine!