I faced the same issue. My bill cycle dates are 19-Nov to 18-Dec and did a plan change on 26-Nov from 45 CAD to 40 CAD.
They charged me upfront $45 in Oct Bill for the full cycle (19-Nov to 18-Dec) and charged again prorated (19-Nov to 26-Nov) as per $45 and 26-Nov to 18-Nov as per $40. But they didn't adjust or gave any credit for the upfront $45 which i had already paid.
Tried contacting customer support multiple times but they went round and round trying to explain something which didn't made any sense.
Did you get any resolution ?
I kept asking the customer service center, but all the agents I talked to said there was nothing they could do, and threatened that if I changed my account, the promotions I was currently receiving would be lost. I didn't try to solve the problem, and it was just automatically calculated, so they told me to stay still.
From your image, it appears as though you changed your plan in the middle of your billing cycle. If that is the case, those are adjustments for the prorated charges for the days those plans were used. You received a credit for the days the 10GB plan was not used. You were also charged for the day or so the 20GB was used ($17.96 - $16.29). The remaining days of that cycle would have been prorated charges for your new, current plan. You can view more information regarding partial and prorated charges here and here.
You should note that this forum is community-driven and not intended as a venue for customer services. As such, we would not have access to customers' accounts. If you would like to discuss those charges, you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀