executing single query in loop increase time every time
What percentage of the 12M rows are you transferring?

This gets slower and slower as you increase the OFFSET:

limit 24000,3000


Instead, "remember where you left off".  More:  http://mysql.rjweb.org/doc.php/pagination and http://mysql.rjweb.org/doc.php/deletebig#deleting_in_chunks

Is there an index on callstart?

The INDEX cdrs_data is a terribly long index.  The only way it might be useful is if it is "covering".

The TABLE cdrs_data -- does it have any indexes?  Of so, disabling the indexes before starting the inserts is likely to speed things up.  Reenable afterward.

Another option is to use mysqldump with a --where clause. for the dump side; then mysql for loading in the new place.