How can I fix this brick?

Without the account information you will have to get your friend who sold you the phone to also give you the receipt from when they (or a previous owner all the way back to the first one) bought it from Apple.

Refer to How to remove Activation Lock - Apple Support There are only two ways to remove a lock:

#1 If you have the necessary information, you or the signed in owner can do this yourself by simply signing in with the owner account and password information and doing as instructed in the above article. If you use this method and this is a new device to you, follow unlocking by doing as outlined in What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support or What to do before you sell, give away, trade in, or recycle your Mac - Apple Support . If you do not have the required information then you can try method 2 —>

#2 Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Read the requirements and steps for an Activation Lock support request at: https://al-support.apple.com/#/additional-support and links at the bottom right for the type of service requested. Apple says they “may” require "proof of purchase documentation” and that you need “proof of ownership documentation”, but does not detail what currently constitutes proof other than it “must include the product serial number, IMEI or MEID.” User reports on this community indicate that typically Apple will absolutely require, and ONLY accept, an original receipt issued by Apple or an Apple Authorized Reseller. Presumably this is the only kind Apple can authenticate against fraud since Apple is not involved in third party sales. Apple recommends that you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support

Note that the device cannot have Lost Mode set on it. If your device has been taken over by you having entered a scammer’s Account then the scammer has likely set that too and the device is lost to you.

If Apple resets the device this will give you access to the device but won't restore access to the account used to lock it. There is nothing that can be done to expedite an Activation Lock request.

If you cannot get the device unlocked then read this section from the very bottom of Apple Trade In - Apple :

"Does Apple offer recycling?

Yes. Apple Trade In lets you recycle any Apple device (including devices from Apple-owned brands) at any Apple Store and on Apple for free. That includes your batteries and old electronic products as well as free, on-demand packaging recycling for our commercial, education, and institutional customers. When we receive your device, it will be thoroughly inspected to determine if components can be recycled or reused. Whether recycled or reused, all activities relating to the processing of your device will be managed in an environmentally responsible way."

And read these for future purchases:

The All Too Common SAD Reality of Buying … - Apple Community

If you want to buy a preowned iPhone - Apple Support

If it's activation locked to an Apple account that has been completely deleted and you are not the original purchaser of the device, it's basically a paper-weight.

There is nothing that you can do about it.

If the person you bought it from is the original purchaser of the device and still has the original proof of purchase, they may be able to get Apple to remove the activation lock.

As for the account, don't let your parents get into the position where they can set controls. I have not seen any way where you can approach Apple with some way of proving you are a certain age. If you are old enough to have a credit or debit card then you can start with a brand new account on your brand new phone that you will be buying because it sounds like you cannot regain control of the old one unless you come to some kind of agreement with your parents.