WTF IINET??!!

A few years ago, we switched to the NBN, and when negotiating the switch from Naked ADSL to NBN, I clearly stated that our phone number was to be ported over to the NBN service, that we did NOT want a new phone number.  I was assured by the sales person that it would be done.
Well, I guess she didn't know how to do it, left the ADSL up and running with our home phone number.  We have been paying for not only ADSL but NBN. Being charged double.
Now, according to our records IINET has overcharged us, over the course of these years, over $2000.
I wonder if they're going to try to find a way to wiggle out of their screw up.