Tab amount, for some reasons, was deducted at different date (compared with the billing date). That was why you might see that. 

What you could do to make sure everything was ok is to download the service agreement in self-serve. Check the 1st payment of Tab and calculate the 24 month period from that month. 

Take a look at this page for more information:

You can also check your tab history screen and post a screenshot of that on here. 

Hello my tab have been paid off and it's still showing on my bill?

When did you upgrade your phone? And when was the 1st Tab amount charged on your account?

Same issue. I can find the service agreement in my self account. :(

It should be at selfserve>>my profile>> choose your number >> my service agreement .