I booked a TPESIN round trip Z class TP run in June and of course my flights got canceled. I call the hotline and the staff advised any rebooking will cost me fare diff around TWD3600
as the price now is much more expensive than I booked during last year October. I said it is not reasonable that MH should charge me the fare diff as it is your side who cancel the flight
(yes I know it is because of COVID-19 but that does not change the fact that it is the airline who cancels the flight) and I am asking to be rebooked under same routing and same class
condition, the staff just say I either pay the fare diff or I can travel in economy or I can complain but the result is still the same.

Should I ask the credit card company to charge back as they fail to provide their service? I read some other posts here and it seems complaining to MH is useless.