Why Am I being charged for a plan I did not request?

I have to write a complaint regarding Verizon's international travel practices.  They have a few different travel plans: one that costs $10 daily, one that costs $40 monthly and a few that are unimportant to this conversation.  I signed up for the $40/month plan well in advance of my travels.  Apparently, even when signing up for the monthly plan, Verizon automatically initiates the daily plan once you leave the country.  I didn't know this and made a few calls on seven different days for a charge of $70.  They expect me to pay this in addition to the $40 I already paid.  I called and they offered me $50 as a courtesy maintaining that, while they do agree that I didn't do anything wrong, the fault was ultimately with me for not telling them of the mistake before I did (two weeks after I started on the plan).  They said it was me who initiated the plan because I would have had to have typed YES when prompted to start the plan.  I have no record in my text log of sending YES even once to any Verizon number.

They also said they sent me daily texts letting me know of the charges.  The texts did not mention anywhere that there was a charge associated with the daily sessions and I thought it was just the monthly plan letting me know it was working.  There was a text I received on the day while I was traveling, but it sounded like an optional feature.  I never activated it.

Verizon needs to seriously improve their international travel plan as it is ridiculous that you can sign up for a plan and have it overridden as soon as you leave the country.