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 $12.88
Fortnite ACCOUNTS USD $3.75
Fortnite ACCOUNTS USD $9.66
Fortnite ACCOUNTS USD $53.68
Fortnite ACCOUNTS USD $3.22
Fortnite ACCOUNTS USD $10.99
Fortnite ACCOUNTS USD $35.99