@Farontothemaddingcrowd - I don't think there's anything wrong with your tone.
I think the problem is, as usual, people don't read the full text and content of your posts, and then pick holes in what they think they've read.
My bank in the UK hasn't issued me with a new cheque book for ages - they told me they'd be phased out by 2020 anyway (guess that hasn't happened yet) so not having a chequebook isn't that big an issue.
The treasurer may have meant to send a revised invoice, and then decided that just sending an email with the bank details was a better plan - but failed to tell you.
You were waiting for a revised invoice to pay, with double check of the bank details on it. This is wise.
I'm pretty certain that YOU had plenty on your plate in the run up to the wedding as well, without needing to be trying to phone someone who you thought was already onto the job (sending a revised invoice).
If it was SUCH an issue, the vicar (or possibly even the treasurer) would have mentioned it AT the wedding - either just before or just after. The fact that they didn't, and you had to contact them yourselves on Boxing Day, shows that either they were thoroughly disorganised or weren't that bothered.
I'm also of the opinion that the vicar "had a word" with the Treasurer and THAT was what set him off - but not being in a position to take it out on the vicar, he's taken it out on you guys instead. Which is utterly puerile of him. I think he also may have the wrong end of the stick and believe that you were accusing HIM of potentially fraudulent activity, which would be miscommunication via the vicar.
I don't think you need to do anything else - it's an unfortunate occurrence, it's done, you've paid, you've sent a thank you, you've apologised, it should now be Over.
Ignore the bitchy comments if you can - there are many MN posters who just love to stick the boot in but there's no need for you to accept that from them.
and congratulations on your marriage - make a NY resolution to leave this matter in 2020, not carry it forward to 2021. 