You need to use the specific application forms.

This is the one for compensation: https://www.easyjet.com/en/claim/EU261

This is the one for reimbursement of your welfare/right-to-care expenses: https://www.easyjet.com/en/claim/welfare

I suspect the £100 holidays voucher is separate to any claim you made, as they have been doing a big marketing push in the last few weeks. I've received two vouchers recently and haven't had any cause to complain for quite some time.