Air Canada - how normal is this?

i'm in 20's , outraged @ moment, maybe i'm being naive, please me out. here situation:

booked trip las vegas months ago air canada , paid $314.32 on credit card return flight. cancelled week later , told can't refund anything, amount "credit". call few days ago book 1 way ticket halifax. i'm told charged $105 "change fees" ($50 each way) cancelling/re-booking flight. notice not deducted $314.32 paid, charged on top of that, have $419.32 on credit card. $105 obvious cash grab , sort of penalty, put aside. issue flight halifax cost $202 including taxes. if deduct $202 $314.32, leaves $112.32 unaccounted for.

make sense far? because when on phone air canada asking them confirm this, couldn't. agent kept repeating fares , taxes different blah blah, wouldn't tell me what, if have left on "credit". kept asking him explain, rude , said did.

i'm wondering:

1. airlines charges these stupid "change fees" , if so, charged on top of paid , not taken credit on file

2. calculations make sense? why couldn't agent tell me what, if left?

3. have tips dealing this? got frustrated agent speaking had hang up..

help!

i'm in 20's , outraged @ moment, maybe i'm being naive, please me out. here situation: booked trip las vegas months ago air canada , paid $314.32 on credit card return flight. cancelled week later , told can't...

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