Unfair billing charges after cancellation of account

I was in Canada and cancelled my Koodo account/subscription before leaving the country permanently. I scheduled a callback a couple of hours before my flight back home, which was in the evening, and asked the Koodo representative to cancel my account from that moment on. I received my Bill today and realised that she went ahead and did so from the beginning of that day because I have been billed for airtime charges for the calls I made on the day of my flight prior to cancelling my account. I have also been charged for a 'Rate Plan Change' when all I asked for was an account cancellation. I do not know how to contact them about this now, since I do not have a Canadian phone number and the only way to contact them is by scheduling a callback. Is there any means of contacting them from an international number or email? Any suggestions are welcome.