The error message you are seeing suggests there is a problem with the connection between the camera and lens.
If you have recently updated the camera's firmware:
This could explain why the lens has only recently stopped working on
your camera. As your lens is made by Sigma, rather than by Nikon, it
could be that Nikon have introduced a change which your lens does not
understand. This is one reason why some people will only recommend
purchasing lenses made by the same manufacturer as the camera. I
would not advise attempting to "roll back" the update, as this could
cause other issues.
It may be that Sigma can update the lens firmware to accommodate the Nikon update. As your lens does not appear to be compatible with the Sigma USB dock you would need to get in touch with Sigma support to enquire about this and/or arrange for the lens to be sent in. (NB: They may ask you to send the camera as well so they can confirm the update resolves the problem.)
If you have not updated the camera's firmware:
You could try carefully cleaning the contacts on both the camera and the lens if you haven't already.
If this is not successful, you could send the lens in to Sigma's service department for diagnostics and repair (particularly if it is still under warranty), or you could take both the camera and lens to a local camera store to see if they can spot any problems with the lens mount which could be preventing it from connecting properly.