I don't have experience of emailing YouFirst, however:
You have paid for first class travel and associated benefits - no reply to your query is not acceptable for even economy travel. I personally would expect a reply within 24 hours.
The fact that this has happened twice would suggest an out of date email address / un-monitored mailbox. I am sure it's not the experience they would like you to have as a First customer.
I would try communicating with them via the phone. I found these numbers ba.com:
In the UK call: 0800 408 7667
From overseas call: +44 161 448 3013