Call UK BAEC for 2 reasons - firstly they will charge you in £ (unlike BA MEX who will charge you in their local currency), and secondly they are the only one that can/will MFU you (as you are a UK BAEC member).
However your location seems to clash with your BA Amex card
There is a dedicated Silver number (still assuming you are a UK Silver) - just log in to your BAEC account, and search for BAEC contact information. Alternatively I am sure that some friendly Silver can PM it to you.