Charging $70 for a $60 plan

I just signed up for the $60/month 5GB DataConnect plan.  But, when I looked at the bill details after I left the store, I found they were charging me $9.99 for the wireless number in addition to the $60 for the LaptopConnect service.  The wireless number is an additional number they added to the account for the data SIM.  I did not actually add any new phone, just the SIM in the laptop.  So, it seems like there really is no $60 plan, because I also have to pay $10 extra for an extra line I don't really get.

Was this a mistake?  Is there some way to actually get the $60 plan for $60? 

Of course, there are also another $16 in taxes and government fees in addition to the $70, so it ends up actually adding $86 to my monthly bill, but the taxes and fees are another story, not what I'm talking about here.