Sorry for my lack of thanks for both your comments here, I lost track of this post!
After returning to the issue, I have found this plugin which does the job great (so far).
Enrolment
Auto enrolling after signup
Αυτή η συζήτηση κλειδώθηκε κι έτσι δεν μπορείτε να απαντήσετε σε αυτή.