@ Nikpatil... try this stpes. may be u did it already but do it for safer side..
1. make sure ur 3G is activated and working by putting ur sim in other device. if 3G not working plz activate it.
2. try to manage other vodafone 3G activated sim card from frnd and try in ur device. if 3G working then repalce ur old sim with new, if not working then it must be 3G settings prob or u need to repaire ROM from PC companion if not rooted.
Android 5.1.1 may be support new sim only for data.. my sim is 7 years old and its Idea.. 2/3G is not at all working. but when i put my frnds Idea sim (which is almost 6 months old) in my phone then its working perfectly on 3G !.. im not sure but i think it is somthing to do with sim type that is h1, h2, h3 etc.. and 5.1.1 support new version only. that is why i suggest you to replace old sim with new after this steps.
