@Wetrix Does your PoF account have a phone number? The fact that she says she met you there tells me she knows for certain you have an account. I would start there. Change the password, remove any identifying information on the account (besides pics, you need those).
If this is not the first time you have had this happen, check where they claim to know you from. It is possible you had some type of data breach on an account connected to all the sources these people claim to know you from