Excesd tax paid in GST

Sir, No one can give acurate reply about GST this reason we cannot doing a business smoothly.Sir my quary we are a LG distributor of Assam Gauhati we have Vat no purchase goods on 15% Vat rate. when GST start we have sold the exting stock on 28% taxes. we have pay extra 13% tax. my quary can i refund this 13%. directly shows Loss . LG not provide Excise invoice .In these what we are doing. sir please reply simly language and understable .