Dear Syed Wasay Ali,
I have been in this situation 2 months ago. That time it meant that I could not get a free exam voucher.
I would like to let you know that the challange page is still (2 months later) showing 8/10, however I completed all, as you did.
Good news is that the system somehow verified the state of the challange and tutorials and I received an email to my MS Learn profile given email account stating "you have completed...". So first of all check your emails and try to find that email.
Secondly, you may check your profile, and the list of badges and trophy's on the main site (Activity), also the Challanges (it shows nothing for me, but I am in a challange, so this is also buggy) on the left side menu, and finally the Achievements (also on the left menu).