I have a licensed acadlt 2009 version of AUTOCAD, been using since I purchased in 2009. I have purchased a licence for the 2013 upgrade, however, when I try to install, it says the 2009 version is invalid + I find out the same serial number is shared by an engineering company clear across the US. I am a retired architect doing small commercial architectural work from home so this is important to me. The autdesk people want a copy of the invoice (from 2009). Can anyone help, thanks