Do not issue another receipt. If you do, unless it's an exact copy of the original, CRA will consider it to be two separate incomes and you'll be taxes on both receipts even though it's only one fee.

Explain to Dad that all you can do is issue an exact replica which was in the Mom's name. Explain to him that their financial agreements with regards to who is claiming what, isn't anything to do with you and you cannot get involved.

But also, until they are officially divorced, and any firm arrangement is made, only the parent with whom the child lives, can claim child care expenses. In this case, that would be the Mom, who has the receipt for 2016.

However, do let him know that once the divorce is finalized, you are happy to write receipts totally the full amount of fees paid, to which ever parent wants those fees. i.e. if they agree to a 60/40 split, then you are happy to write 2 receipts one for 60% and one for 40% as long as the total isn't greater than the fees paid. I'm not sure who can claim what after divorce but you need to be clear that isn't your concern, that you'll write receipts to both, or to one IN FUTURE but you cannot divide the 2016 receipt this late in the game.

His tax fraud in claiming when he doesn't have a receipt, isn't your concern. It isn't your responsibility to create paperwork that supports his fraud.