I bought a iPhone from someone but they are still logged into their iCloud and iTunes , the person doesn't remember their password and now I can't get hold of them. I want to erase the phone and start from new

If you are trying to activate an iPad or iPhone and it is asking for a previous owners Apple ID and password, you have encountered the Activation Lock. This is a security feature that prevents thieves from setting up and using a stolen or lost iPad or iPhone. You have no alternative. You must contact the previous owner to get permission to use the device. If you cannot contact the previous owner return the device to where you bought it and get a refund. You will never be able to activate the device and no one can help you do it.

as I can contact with the owner of the only cases in ID icloud I have nothing but ... help ... cell block this with icloud

They need to remove the device from their account. It's the only way and there are no workarounds. No one else can help you.

So contact the previous owner and ask him/her to follow the instructions in this document:

Turn off Find My iPhone Activation Lock - Apple Support

Yes, you have a problem. Unfortunately there are no known workarounds for this. For future reference, do not hand over any money for any Apple device until you know for certain the previous owner has signed out and that you can take control of the device with your own Apple ID.

With out the Apple ID and password, the phone is useless. You have a brick.