Hero Motocorp — Faulty servicing by nawander motors, amravati and then not accepeting the responsibility

Address:

Amravati, Maharashtra, 444601

I have purchased hero i-smart from nawander motors (Authorised dealer of hero motor corp), amravati, maharashtra after that during the time the servicing there is lower nut down the fuel chamber is fixed with m-seal now that there is oil leakage through hence again i took my vehicle to nawander motors but the company manager is not accepting his mistake. So please suggest me what to do now and how to resolve this issue...