There has been a couple folks with a similar issue.
Your best bet is to troubleshoot. Try restarting your phone first. If that doesn't do the trick and you have a local AT&T/Microsoft Store nearby you can go try their display wireless charger. That will narrow it down to a faulty charger or the phone at least.
One other person said that the coils in his phone were broken so he had to get a replacement phone before it worked.