Hello @ EmmaE99

I seem to have the same issue. My companion voucher will not appear when I try to Book for a flight with Avios like the screen grab from AJA. The voucher number is also has 7 digits just like yours.
I will like to inquire if you've been able to resolve it or if you were lucky to get a response from BA, so far I have been chasing my tail on this issue.

My voucher is due to expire next year April.