Poor Customer servicr

I have registered online to sell my car to we buy cars.From the start ot was poor customer service with the CT branch.The guy promise to call back then never do.I had to keep messaging to remind him to call me.How do they get business like this. Then after making contact there was some questions re the vehicle,which I didnt mind.But when he told me that they will need to see my invoice from who i bought and he asked my how much I paid etc....That all after i told him the car is registered on my name.I bought at an auction.I do this on my private time as I have a business set up already. Then I mailed their customer service to find out why they want all these peraonal details after I told them the car is on my name and all the paperwork is correct.They must just do their inspection and once they agree to buy they can and will see that the paperwork is all in order.If my previous invoice from who i bought it and how much I paid was questionable how on earth did I get it right to have the car registered in my name.I am wondering if they know the rules of purchasing a vehicle because of this silly personal questions they ask after being informed that the car is registered on my name