If you have the time, please check out my message from another post - I'm all messed up at this point:https://xoops.org/modules/newbb/viewtopic.php?topic_id=60057&post_id=289407#forumpost289407

Don't panic...... we'll sort you out.

Try the advice in the other post first.

What version of XOOPS are you using? Just for my benefit if you need more help

Edit 2 files to remove the registration link

This is for your user.php page
/modules/system/templates/system_userform.html
Comment line 11 as below
<!-- <div><{$lang_notregister}><br /></div> -->

This is for the login block
/modules/system/templates/blocks/system_block_login.html
Comment line 14 as below
<!-- <a href="<{$xoops_url}>/register.php"><{$block.lang_registernow}></a> -->

If you have already disabled user registration in system>preferences then don't worry about someone going directly to your register.php page because they can't register.