ipad activation lock

I had not realised my phone and ipad were linked and changed my iphone password this morning. When I try to turn on my ipad it goes to activation lock and is looking for Apple ID which is prompting me start of my username but ending with gmail.com. my apple ID is the b.....@icloud.com when I enter in the b.....@gmail.com username it tells me this is not an apple ID. I have tried the b....@icloud.com and it tells me that this ID cannot be used to unlock this ipad. I cannot remember what was my old password (which is why I changed it. Any solution?