I bought phone and it was dead he said it was open but it was t now I just want to get it unlocked

If you have bought 2nd hand iPhone, you must contact the seller (hopefully it is the previous owner), otherwise you have been scammed.

Each Apple device is linked/associated with an Apple ID of the person who did the setup.

Activation Lock prevents anyone who is not the owner from using this iPhone.

To unlock the Phone, you need the Apple ID and password of the previous owner, that were used during set up.

So you have to contact the previous owner.

The previous owner has to read -> this Apple article: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch -> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Then the previous owner has to remove the iPhone from his account, see this Apple article:

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to find where you're signed in - Apple Support

Then you can sign in with your own Apple ID.

See the following Apple articles:

Activation Lock for iPhone, iPad, and iPod touch

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

How to remove Activation Lock -> How to remove Activation Lock – Apple Support (UK)

• If you need help removing Activation Lock and have proof of purchase documentation, you can start an Activation Lock support request.

Read this before you buy a newer iPhone.

You can also contact Apple support for help, -> Get Support (apple.com)

You have to show proof of ownership of your product, provide all documentation showing your purchase of the device.

If you do not have additional proof of ownership, contact the reseller. They may be able to provide the original purchase document.

Once Apple receive your proof of ownership, Apple will further review your request and provide an update.

Ask your money back if possible.

Chào bạn! Giấy chứng nhận bảo hành thiết bị cho ID apple của tôi có thể chứng minh quyền sở hữu thiết bị không. Giấy chứng nhận bảo hành thiết bị cho ID apple của tôi có thể chứng minh quyền sở hữu thiết bị không.

I've contacted support so many times. They were really enthusiastic and wanted to help me. I've also given a personal opinion on whether Apple might have more flexibility in verifying device ownership beyond the purchase bill. Because I am a new user who is not very clear about many of my regulations and rights. I only have warranty product information on my Apple ID. I'm willing to provide location information as well as activity logs as proof. But it's all pointless

Check here -> Keep your receipt after you buy an Apple device

Keep your receipt after you buy an Apple device – Apple Support (UK)