On your Electric Car Scheme Employer Portal you can find all invoices from ECS.
Invoices from the lease or subscription provider are NOT included in the ECS Employer Portal. Those will be sent directly by them to the company. You can find their contact details here: What are the contact details for the car provider?
How do I find them?
Simply go to the Employer Portal, click "Invoices and Payroll".
Downloading "invoices" will download a pdf copy of your invoice from ECS. Make sure to select the relevant month and year.