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 $21.47
Fortnite ACCOUNTS USD $2.15
Fortnite ACCOUNTS USD $64.41
Fortnite ACCOUNTS USD $85.88
Fortnite ACCOUNTS USD $3.22
Fortnite ACCOUNTS USD $15.99
Fortnite ACCOUNTS USD $3.76
Fortnite ACCOUNTS USD $37.57