Help....We went in to buy a new phone - a Samsung ...

Help....We went in to buy a new phone - a Samsung 8 - and came away with an extraordinarily expensive mess that is taking days to fix.
We were given a 'free' Nighthawk modem to connect to the internet. (Its actually not free at $45 a month.)
We were advised that we would not need our present wi fi and on that advice we disconnected it.
But... the new Nighthawk system didn't work in Beechworth and left us with out any internet access at all.
We were assured that our new system would be cheaper..only $150 a month but now we look like paying $250 a month.
Five days later it is still a mess and is becoming very expensive (to get reconnected) and a lot of time consuming phone calls to Telstra to try to sort out this mess.