what can i do if i forget everything about the apple id that I set my iPhone with, and my iPhone now is activation locked?

If necessary, if you are the original owner, take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store.

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or contact Apple ID Support. They will need to see the original purchase receipt/paperwork also.

Apple ID Support

Apple ID Support (2) 

Apple Support by e-mail or chat         

Apple Support using Twitter

Or fill out and submit this form.

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