Get in touch with them, I had the same trouble when I tried to register my copy of HELS a short while back after realising I never had. The customer service lady registered it for me no trouble.
As for wrong serial numbers my base game was registered with the old EADM system, when I visited England in September I downloaded it from my games in Origin and put in the code it has listed, same as my dvd one I registered and it told me it was invalid, the system is a little faulty at times but they are usually helpful at sorting it. I admit I didn't contact them then I just used my neices dvd instead but I'm sure if I had they would have fixed it as they did my HELS one.
I emailed them but then I wasn't in a hurry, they surprised me though by answering within a very short space of time saying it was all sorted for me and my game had been registered. So if you don't have time for a phone call or live chat email works too.