well in my opinion you should call customer care it look like your plan is on auto-renewal thats why it deducted balance and it went to negative ask them to cancel that auto-renewal plan so that you can choose plan of your choice. same happened with me after 30 days of purchase balance went to negative 700rs. I lodged a complaint via email to cmdbsnl@bsnl.co.in as local employees were clueless about this. Got response from them and they deactivated auto-renewal then I did recharge of my choice