IPhone Call Log and encrypted Backups

Hi, I am trying to find an a record of an incoming call that no longer appears on my call log (IPhone6, IOS10). I have tried numerous free versions of software that claim to be able to access records in ITunes backups. My backups are encrypted and I know the password but all of these programmes give an error when trying to decrypt. I cant turn off the encrypt backups option in ITunes. Can anyone suggest how I can either access these old call records on my phone or how I can recover them from encrypted backups? Thanks, Julian