Apologies to hear you are having trouble! Sounds like there might be two issues at play:
- When importing batches, WordPress is told to increase resources allocated to PHP, unfortunately some host do not honor or hard limit resources. This is a bit rare. The symptom of this would be less than a 100 would be imported.
These are just my guesses based on the description of the issue. If you give me a temp admin login, a copy of the CSV file with a screenshot of the mapping step, I can log in and take a look. The details can be posted here as a private reply.