Can't cancel without 6-digit passcode

Can't cancel my service without going into a physical T-Mobile store because IDK the 6-digit passcode I set it up with over a year ago. There's really no possible way to confirm that I am me without a 6-digit code?

Easy to sign-up, but hard to get out. 0/10 won’t ever recommend.

Good luck getting anything more from me considering how the company has gone so far out of it's way to financially mess with me previously and now again. Obviously should've learned the first time, but here we are for the last time.