I am sorry you are upset by this.
The regular price for the exam is $99, we ran a special offer for Black Friday where the exam could be purchased for $9 (
https://portswigger.net/blog/burp-suite-certification-prices-hacked-for-black-friday). This offer was due to finish on 30 November 2021 but due to some server maintenance at the end of the month, we extended the offer until Thursday 2nd December 2021. I'm afraid this was a time-limited offer. We communicated the offer on our blog (see the linked post above), and shared extensive posts regarding the offer and the extended deadline across our social media channels.
I apologize that you are frustrated about missing the offer, but unfortunately, there is nothing we are able to do about that.