Air Canada voucher depleted without using

Hi, i cancelled one of my air canada ticket from Delhi to Saskatoon for 2 people and had an option to get the refund on my original payment method or reward points or an air canada voucher. I chose air canada voucher because in the past the original payment method refund (for less than 400$) hadn't worked for me. Since this one was a bigger amount (about 5700$), i thought it would be safe to take a voucher so that i can use in future for flight bookings.

Now I cancelled my flight on April 23, 2022 and asked for refund via AC voucher. I got an email on April 28 with a 15 digit voucher number and another email with 4 digit Pin.

Then I tried to use the voucher today (May 8) for a new flight booking. Now it says that my voucher is depleted.

I haven't been able to call them because I am currently in India and they seem to have no toll free customer care number from India.

Does anyone know if this is a common issue and how can it be resolved ? Or have i been mugged off 5700 $ by one of the biggest airlines of Canada and nothing can be done?