Please take each of the following steps that you haven't already tried. Stop when the problem is resoved.
Step 1
Mail associates a name with an address by looking up the address in the Contacts database. Do that yourself and correct the entry or entries.
Step 2
If the wrong name is associated with your own address, select your card in the Contacts application. Then select
Card ▹ Make This My Card
from the menu bar.
Step 3
Delete the unwanted address from the Previous Recipients list under the Window menu.
Step 4
The spelling checker may be falsely correcting the entry. Please select the incorrect entry and right-click or control-click. From the popup menu, select
Spelling and Grammar ▹ Show Spelling and Grammar
A small window will open. In the text box at the top, enter the incorrect text, then click Change and close the window.
Step 5
Quit Mail and Contacts. Back up all data.
Triple-click the line below on this page to select it, then copy the text to the Clipboard by pressing the key combination command-C:
~/Library/Application Support/AddressBook
In the Finder, select
Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You may not see what you pasted because a line break is included. Press return. A folder named "AddressBook" should open.
Inside the folder there should be one or more files with a name beginning "AddressBook-v22.abcddb". Move those files to the Trash. Launch Contacts, then launch Mail and test. You might have to log out or restart the computer in order to see a change.
If the problem is resolved, empty the Trash.