I think the POST request you made wasn't handled by your servlet.
Look the code of SlingProprtyValueHandler: src of SlingProprtyValueHandler
CQ doesn't use your servlet, so it thinks at "/bin/feedServlet" there is a resource and it tries to modify it (because it is a POST request), but there is not any resource, that's why you got an exception.
Please create a doGet method for your serlvet and try to make a get request, I am sure that it won't work.
Check your servlet is active or not under /system/console/components.
You can also check whether the /bin path is allowed or not under /system/console/configMgr/ check "Apache Sling Servlet/Script Resolver and Error Handler".
I hope this helps!
p.s. It is better to map your servlet to a resource instead of a path. example code here how to map a servlet to a resource
So you can create a a path like /etc/myApp/services and under this path you can create a myService node with a type like etc/myApp/services/myService, and you can map your servlet to this resource type.