If you are failing to reach the seller that sold you this iPad so you can elicit their help or to return this iPad and get your money back, then there is nothing more to be done.
You purchased a dead, useless device to you.
You'll never get that iPad to work for you without the aid of the previous owner of this iPad.
Failing this, there is nothing anyone here can do to help you and Apple WILL NOT get involved with any of its devices that is user activation locked to another owner/user.
If you cannot get this iPad working, please recycle the device responsibly.
Hopefully, you didn’t pay a lot for this iPad.
Next time, If you purchase another iPad, then, you need to purchase a new iPad from Apple or a discounted, refurbished iPad from Apple’s Refurbished & Clearance section of Apple’s Website or a new or refurbished iPad from an Apple authorised, third party retail or online reseller OR other trusted sources for new or used Apple products.
If you must purchased used devices from unknown sources, you must ask more questions of the iOS device seller, ask for more photo/images, ask if the iPad has user/iCloud activation lock and ask for photos/images/short video proof that such an iPad has been reset factory settings and shown proof of the iOS device's start up screen showing the animated, moving, multi-language “Hello” Welcome to iPad screen.
If the iOS device seller is unwilling to do all of this, pass on the iOS device and look at other iOS device sellers.
Also, make sure the iOS device is something that is fairly recent as all older 7, 8 and 9-year old iOS devices have no more support from Apple or third party apps from the iOS App Store.
Sorry & Best of Luck to You!