I opened my iPad on December 8, 2017 to find Activation Lock turned on. I have tried every suggestion to fix this and nothing works anyone else having this problem?

I have an older iPad that is now unusable because Activation Lock has turned on for no apparent reason. I went online and turned off, Find my iPad. I tried activating my iPad but it won't recognize my Apple ID or Password. I may have used a different Apple ID when I purchased this iPad many years ago which I don't remember anymore. I have connected my iPad to my Mac computer and restored my iPad and I am still unable to unlock the Activation Code. What else can I do to resolve this issue to unlock my iPad?