thanks everyone for your replies. here's where we stand:
i found a friend that has MCP gold status and asked him if i could use his member number just to get to talk to a human being. without it, there is no other option to reach a human being.
so it worked and i spoke with a rep. she said all was okay on their side and she didn't understand why i was getting that error message. i was also told that we are assigned 1A and 1D which, on a 777, is not ideal and they can't change it since it's a BA booking. i talked to BA and they said they can't change it either except to give us 1 & 2 D since the A & K seats are all restricted. the dumb thing is that if i go to the CX website and make a fake booking, i can select 1K
and now, for some reason, i can't even get into my booking anymore and am getting an "internal error" message on the MMB page. i'll just have to wait until tomorrow, or maybe tuesday, and try to reach reservations again.
i'm flabbergasted at how opaque these systems are. i can't log in, i can't talk to a human without "cheating," i can't change my seat, MPC can't change my seat, BA can't change my seat. And to top it all off, the F section of the wing is closed for remodeling. this trip is a very special occasion for us and is already beginning to get a sour taste to it. i really hope it gets straightened out and that everything goes smoothly.