Apple ID and password on a phone I bought can’t get on phone and the previous owner I don’t have their details.... help!!!

If you are the owner of the iPhone or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner of the iPhone and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password to you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their apple ID.

It won't help Apple can't or won't do it.

You need to go back to the seller and ask them to fix it for you or refund you (if they are a reputable seller, they will do this). If they won't then if you bought on an online platform that has buyer protections, you need to open a dispute. If you bought privately or from a dodgy seller, your only recourse will be the courts - which probably won't be worth it.

That could only work if you had the original proof of purchase. I'm guessing you don't. A bit of paper from whoever you bought it from isn't going to cut it.