Sometimes ticket is not issued concurrently/immidiately after you complete the reservation of the flights. This occurs often if you call to reserve; hardly never if you make booking online.

In order for you travel there needs to be a ticket associated with the reservation and if you make a last minute reservation like you apparently did, you can end up in situation where no ticket has been issued yet when you try to check-in; either online or at the counters.

It appears that the CS representative that you talked to, forced the ticket to be issued.

There were severe weather distruptions across parts of Europe in the past weekend, it sounds if the FR flights was affected by that. In the afirmative, there is no obligation on the part of FR to pay compensation, whereas any disbursement should reimbursed. However, I'm not sure if FR is going to refund super expensive last minute BA tickets to the UK. You may have much better and quickler luck with your travel insurance. Good luck!