Hi everyone, so this is my problem

I have clip studio paint EX (when i bought it then it was still manga studio), the 1.5.4 version and the only trace of it I have is that serial number (wich they won't let me see in full) that i can't retrieve. At the time i believe I didn't even had an account, i just bought the key and entered it on my old computer and it is still active on this computer but i have no account linked to it it seems.

I sent a message to the support but I'm not really confident that it will lead anywhere. So, having searched before on the forum I'm still trying my luck here
Is there anyway to retrieve my key (in full) on this old computer or evantually if there was a account liked(even if i don't remember making any) to it find this account ?

Thanks in advance.