I recently bought a new phone and the last owner said he got locked out of his account and had no access to it what should i do because now the device is activation locked?

You acquired the phone second hand from an individual. The following information explains what has happened. You apparently didn't know to heed the advice given below.

"Before you buy/acquire an iPhone, iPad, or iPod touch from ... [a third party], make sure that the device is erased and no longer linked to the previous owner’s account."

And see: Activation Lock for iPhone, iPad, and iPod touch https://support.apple.com/en-us/HT201365.

See this heading Check for Activation Lock before you buy/acquire a device from someone else.

The presence of activation lock means that we can't help you. We are not authorized to remove the activation lock from any device. And, under your circumstances, Apple support will not remove it since you cannot provide proof of ownership that they will consider to be sufficient. You would need and have your purchase receipt for the device from an authorized Apple seller with the device's serial number on it.* 

If you can't contact the prior legal owner and don't have the receipt, the device is useless to you. Note that the person you call the last owner is not at all likely to be the prior legal owner. Also, there is no way to trace down anyone having the phone prior to you.

*Rarely, an iDevice is purchased activation locked from an authorized Apple seller.

Activation Lock Problem

If you purchased the device second-hand, then it is useless without the Apple ID and password to which it is locked. If you don't have it, can't remember it or cannot get it, then the device is useless to you. Try to get your money refunded, if you can, or take it to an Apple store for an exchange provided they will help you. If you are the original owner, then take the device, a copy of your purchase receipt and identity proof to an Apple retailer where they may be able to assist you. For a deceased owner see How to request access to a deceased family member's Apple accounts - Apple Support. Note: there is no guarantee that anyone can gain access to the device.

About Activation Lock on your Mac - Apple Support.

Activation Lock - Turn off Find My iPhone.

About Activation Lock on your Apple Watch - Apple Support.

Turn off Activation Lock - Apple Support.

Need  to  disable  Activation  Lock  on an  iPhone  or  iPad?