Xianning train to Changsha or Shaoyang, and then in Changsha, you can take a bus to Wugang at the South Bus Station, and there seems to be a direct bus from Wugang East Bus Station to Weixi, and then in Shaoyang, you can take a bus to Wugang at the East Bus Station.
If you take a bus to Chengbu from the two places mentioned above, you should get off at Xiyan and then transfer to Weixi
.