There seems to be a difference between the available Store Credit of yours with the site currency you had picked previously. Would you like to:
Fortnite ACCOUNTS USD $8.71
Fortnite ACCOUNTS USD $21.78
Fortnite ACCOUNTS USD $54.45
Fortnite ACCOUNTS USD $12.52
Fortnite ACCOUNTS USD $49.99
Fortnite ACCOUNTS USD $81.67
Fortnite ACCOUNTS USD $76.23