Vodafone India — vodafone centre service

Hi
My mom is using a vodafone sim from last several years, few months back she linked her number with adhaar card. Again, after few weeks she was asked to linked again, which she did though. Last month, when she visited the vodafone centre for recharge, she was again asked to link number with adhaar, when she went to office after 2 days to get it linked, a different employee told her its already linked and sent her back. Again for the fourth time, when she visted for recharge, she was told that her number will be deactivated within few hours if she doesn’t switch from prepaid to postpaid and link it with adhaar which means every month she has to pay more bill than earlier. I want to know why vodafone is doing this? Are the employees doing this to fullfil their target by looting innocent people? I believe this practice is against the law to force customers to switch from prepaid to postpaid. I appreciate your earliest reply.