Is the OP entitled to FTV?
They mention the book date being September 2019. The way I read the book with confidence voucher eligibility is if flights are booked after March 2020. Or is FTV different to travel with confidence?
Taken from BA.com this evening:
Cancelling your booking
If you decide you no longer want to travel, you can cancel your booking and we’ll give you a voucher to the same value for a future booking (applies to bookings made from 3 March until 31 August 2020 for journeys that are due to have been completed by 30 April 2021).