Recover Email for Xbox Live (I’m being charged for a service I don’t have)

So in 2010 I received an Xbox for a gift. When signing up I didn't have a Microsoft account so I made a quick one up and had everything on the Xbox saved and I eventually used auto renew which my girlfriend at the time was paying for. So everything was fine untill a year ago when my house was burglarized and my Xbox was stolen. So a few months passed and my girlfriend realized that shes being charged by Xbox. So I called and Xbox informed me that they couldnt do anything unless I had the original email. Well the problem is I don't remember at all due to the fact that I never used it and it was stored on my Xbox. So how can I recover that email so Microsoft can stop billing me for something I don't have?