As per the form 245 is the start of your account number. This is not the same as your credit card number.
From Avant:
"Your 16 digit credit card account number which begins with 245. This is different to your card number and you will find it on the top bar of your online account Using any other information as a reference will result in your payment being returned."
If you're using your phone to look for it make sure you've enabled desktop mode.