I missed my flight on BA

I am sorry you missed your flight and understand your frustration. How did you miss your flight? Did you get to the airport late (maybe due to an accident or train problems)? If so, the airline is not obligated to give you a refund. Or was your first flight late, hence you missed your connecting flight? In this case, they should have put you on another flight to your final destination without additional cost to you.

1) check the t&cs of your booking to see if you are entitled to a refund. If you are then follow BA’s complaints and refunds policy. If you aren’t entitled to a refund move to 2).

2) buy another ticket.

Not knowing the circumstances of how it was you missed the flight makes it impossible to give relevant advice on how to proceed.

Please provide some details and your chances for helpful advice increase greatly.

As the others have indicated, no one can help you without the details.