Fou wheeler-Taken by Bank

Sir, I have taken a four whleeler loan from HDFC bank, Durgapur, West Bengal. Because of some reasons, I could not pay EMIs and I handed over the vehicle (honestly I don't know that banks should not take back vehicles from their consumers, if they default). They did not give any receipt after taking the vehicle back. Concerned employee of the bank, told me that they sent notices, before and after online auction of the vehicle. I could not receive the notices as I changed my residence. They told me they got the vehicle valuated and sold through online auction and they sold for less price than outstanding payable by me towards the vehicle, and I need to pay the loss amount to the bank. I am asking them for photocopies of notice, and sale deed for at least 4 months. They are telling me, they don't have copies of notice and sent a requisition to its Head Quarters in Mumbai for the scanned copies of notice. They are repeating the same answers. My questions are: 1) Are their arguments valid? 2) Can I get my vehicle valuated comparing with vehicle in similar condition, by a third party? 3) If I don't pay the loss amount, they are saying, they file a civil case on me. In such case, what will be consequences on my job?(I am working in Central Government Organization) Thank you.