Hello, thank you for the question. I have dealt with this before.
While it's tempting to say that one should be entitled to deduct from child support the amounts owed back to you from the support recipient for s.7 expenses, I don't recommend you do that. Yes, it should all come out in the wash. But child support is child support, and expenses are something else. Unless your court order or agreement calls for you to be able to make that deduction, you'll technically wind up in arrears of the child support. If you're paying her directly rather than through provincial support enforcement, you'll likely find that she registers with enforcement in order to get around your deductions. If the support is already being provincially enforced, your deductions won't be recognized by that agency unless the court order or agreement allows for that.
A court order would be the cleanest way to fix this, although going back to court is a pain. What you need is an order that she co-operate with your access to her benefits directly. Orders like that can be dicey because each benefits plan is different.
Unless your ex enjoys going to court, this is something you should be able to work out with each other. I recommend as a first step getting a lawyer to write her a letter. A simple letter shouldn't cost much, just to get it started, and if you have to take it to court the letter will show that you tried to resolve it amicably but she didn't co-operate and you were forced yet again to go to court. The letter should remind her of her ongoing obligation for income disclosure (I hope you're providing yours, otherwise it turns into a he said / she said where each blames the other for not disclosing and that's why they didn't disclose) and offering to open a dialogue on how these expenses should be addressed, failing which you'll be going to court again and vigorously seeking costs for the unnecessary litigation.
She's obviously not in the mood to be co-operative with you, so don't write the letter yourself. Get a lawyer to do it. She's more likely to pay attention to it and know that you're serious.
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