I'd be chasing that up ASAP, I would probably call rather than email - aside from the work experience form, the same email also gives you links to 2 other questionnaires and their deadlines were the 25th of October, with them explicitly saying failure to meet this deadline without mitigating circumstances leading to your application being declined. If you can prove you did not receive an email that may be a mitigating circumstance, but I'd chase it up sooner than later and definitely check all spam and junk folders, and be checking you have the correct email in your UCAS application.
Best of luck!