Although as of today I have had no communication from Amex, a google search came up with the following:
The current programme ends on 1 November and Amex is offering Brussels Airlines cardholders new cards with membership reward points, but unlike the old cards these are not free for SEN.
These points can be exchanged for M+M miles.
Miles will still be awarded for transactions with the old card until 31 October and it will then be cancelled on 15 December.
Details here in French and Dutch:
https://www.americanexpress.com/fr-be/cards/switch/
https://www.americanexpress.com/nl-be/cards/switch/