Cars Q&A

I have purchased second handle Hyundai Accent GLX car in Mumbai and have use it in Bangalore. I need to change the registration of car from Maharastra to Karnataka. I visited RTO office and they told me apart from RC book, NOC and Insurance they require that Original Invoice of the car at the time of purchase which I do not have nor my previous car owner. The RTO require this to check the Ex-show room price at the time of purchase in order to calculate the Road tax here. I am struck here. So please guide me how to proceed.