The golden rule of cashback claiming is to read the rules, I am afraid.  Even though you didn't actually read the T&Cs, what they say holds true for you nevertheless - if you think about it, it couldn't be any other way.

So this is your error and not theirs; you have failed to give all the ciorrect information, which you must do before being timed out. 

The small claims court would not hear your case because there is no case to answer.  Sorry.

Cat