new regirstation code ?!

Hi there !

I bought cubase 7 about 6 months ago and now that i want to upgrade to 7.5 and entered my registration code i’m told that i can’t upgrade because i have already used it once and i need a new one ?!
to whom should i contact about it and how ? how can it be fixed ?
pls need your help

You entered which acvtivation code? The C7 one, or the C 7.5 one?