Supervisor who accepted me for a research internship now says he doesn't know who I am I've been accepted in a research internship. However, after I sent an email to my supervisor asking about some details, he told me that he has no idea about who I am, and that maybe I've been exchanging with someone else. But the confirmation letter was signed by him.
I'm so confused, I'm afraid if I send more emails it would look like I'm forcing things. I'm really confused because I refused many offers to work in this lab. Any suggestions please?
I would send him the signed documents in e-mail, asking him if it was signed by him. His answer would shed light on things (he forgot he signed, he didn't read before signing, etc.) 
But don't think that you're pushing things. An internship is important, and you already got a signed document and you need to know things to plan forward...