Vodafone India — negative balance in vodafone

My Vodafone 3g sim has balance of rs.196.49 .When I upgrade my sim to 4g it shows the sim balance is RS.-196.49.I have not activated any extra value added services .I talk to Vodafone customer care and go to Vodafone store in Krishnanagar, nadia district, West Bengal, India.They cannot tell me the reason behind it.My number is very important.I tell them how to get the positive balance they say that you buy a new sim or buy unlimited plan
.but they don't give me the surety that my sim balance will become positive.