former student ID vs old student ID

[kwfine]

Dear Alan,

Happy New Year!

Recently, I lost my library card of ABC School.
Although I have graduated from ABC School, I am still keeping my ABC School student card in my wallet.
The student card ID is the same as the library card ID.
I want to report this incident to ABC School, but when writing the email to them.
Since I have graduated from ABC School, which of these sentences is the most natural and accurate?

(1): My former student ID was 12345678
(2): My old student ID was 12345678
(3): My student ID was 12345678

I am so confused of the first sentence because it sounds like that I ever had a student of my own whose student ID was 12345678.

Thank you.

Kitty

[Alan]

Happy New Year!

All are possible and contextually interchangeable. #1 is simply the most formal.