Venus, the support email is on the website (see eBook Help at the top of each page)...
ebooks_techissues@harlequin.ca
eBooks_ecare@harlequin.ca
I don't know if calling will get things fixed faster or not.
It seems everyone is having their account break after 4 purchases (the books are there, you just can't get to them [I download each one right after purchase in case I get locked out again]. Once fixed (it's been taking a few days) everything seems to go fine.