I too struggled to get an assessment date when invited.
After checking several times a day for weeks I've emailed the standard EasyJet email and received a response which is both disappointing and frustrating.
They currently have no assessment dates available and aren't planning anymore any time soon.
They've assured me THEY will get in touch with ME when dates become available. They will keep my application on file for 12 months.
Why oh why would you invite someone to assessment only to not be able to provide them with one?
This is a PFO in my book. Sorry to be the bearer of bad news.