How to find my contract number?

Hello. So I want to cancel my Bouygues Telecom universal mobile plan, I know the procedure, so that's not an issue, but due to my flawless organization, I've lost the paper regarding my registration that contains my contract number. ^^'
I tried calling customer service, but they don't really seem to be glued to their phones, so I can't reach them.. >>'
Apparently, on the website, you can get a consumption statement where my contract number could be indicated, but it's paid and honestly a hassle, plus I don't see why I would pay for it to be honest.. -__-'

If you have a solution to find a contract number without too much hassle, that would be great :)

Thanks in advance.