Why are you getting copies of your ex wife's personal transactions from your step daughter and does your ex wife know her daughter has been giving you copies?
If you've asked your step daughter to get copies for you without your ex knowledge that's bang out of order, if your step daughter has taken copies herself without you asking, then she is bang out of order too and you shouldn't have looked at them and told step daughter not to interfere in her Mums personal finances.
You do realise you don't get to control how your ex manages her finances, you don't get a say in how much her housing should cost. You don't need to know why she rents instead of buying because it's absolutely none of your business at all.
Contributing to your own child's costs doesn't give you entitlement to know the other parents financial ins and outs, younsiund very much like my Dad, he would stop paying the pittance he already paid if he got wind of Mum buying anything non child related, like a duvet for her bed, he and his wife would question us at contact about Mums coming and goings he'd also say our clothes were tatty and old, they weren't, he just had some stupid idea that Mum should use the pittance he gave her to buy a selection of expensive outfits for when we visit him, even though he never actually took anywhere because again, he said he gave Mam money for that stuff, where is she spending it if she can't take you out, etc etc.
You sound finacially controlling, you really do, if you had genuine concerns about her not meeting your child's needs, housing, clothing, feeding etc, then you'd have raised concerns with relevant authorities, it sounds like you just don't like not having a say in how she spends her own money.