Safari Autofill is using the wrong Contacts card
Check that the correct card is selected as your "Me" card in Contacts. Open Contacts and select "Go to My Card" from the Card menu. If the wrong one is selected, find the correct one, select it and mark it with "Mark This My Card" from the card menu.

Within Safari Preferences you could also check the AutoFill tab. Make sure "Using info from my Contacts card" is ticked.