Did you get the desired number in the end?
I just was struck by this lightning here …
Shows you what I know, really. I didn’t realise the file format of the backup was simple to deal with.
So, if you wiped the phone before dealing with the calllog.db, and if you have your TWRP backup on a computer, then just open data.ext4.win from the backup with e.g. 7-Zip (Edit: for Windows , the tar command works for Unixoids) … this should show only a folder (without a name in my case, but this could perhaps be different), open that … and there you are … data/com.android.providers.contacts/databases/calllog.db.
I learn every day 
.