Try
MortPlayer. The app info on Google Play specifies that it can play WMA files, "but only on devices which support them." What device do you have?
The PowerAmp website says it plays most WMA files, except certain WMA Pro files that require NEON--I'm not sure what that means.
Also, are your WMA files DRM copy-protected? If they are, they probably aren't playable if you copied them over from wherever they were. If you ripped the music from a CD into WMA files, then they shouldn't be DRM protected.