I just tell them I was overpaid, and I would like to give back the money, that’s it, cause it is a big company, so they have their own process of it. They just need to fix it in their system, and do some little extra work, like give me a new pay stub something . And honestly, CIC has no access to CRA, only if when they feel something suspicious, they would contact CRA to verify it, don’t be too stressed out. That’s just couple of hours, it won’t affect you, cause I was like that, but I called 3 different immigration lawyers, I got the same answer, CIC doesn’t have access to your tax information. Unless they feel something suspicious, they will contact CRA. But I was still worried, so I just said I was overpaid, and gave back the money. But technically, you shouldn’t have any problems