So another unexpected update. I tried the transfer again this morning and I already have an email confirming the money has been sent to the receivers account. We haven't actually got the money yet, but that email is as good as confirmation and it will most likely be there today. So this time a turnaround of under a day. Another thing worth pointing out is that this time we didn't even receive the registration form that they've sent multiple times with every other transfer.A quick update for those having trouble sending to bank accounts, after two rejected transfers, a third that we sent on Monday the 18th went through today. I'm not sure if there's a reason or if it's dumb luck. It obviously took a little longer than the first ones, about the full six working days. I'm going to send another tomorrow to see if that is also successful and will report back, I'd recommend anyone that was having the same issue try again, with any luck maybe they've sorted it.
It's worth pointing out that on the day I sent the transfer last week, in addition to filling out the form they sent automatically, we filled out a seperate form that we got from the infomation you receive when you phone western union - https://www.e-pagofacil.com/dtb/ - What this is supposed to be for is to allow people who have received money as a cash pick-up to instead have it deposited into a bank account to save them having to pick it up. First you register using that form, then send a email with your details to WU to request the money. We were planning on trying this as an alternative to a direct deposit, once you fill out the form you're told that you'll get a confirmation email in 48-72 hours. (If any one wants more info on this it's all in the recorded message in spainish you hear when you phone WU's argentinian number) We never received the email, and therefore never tried it to see if it worked. It might just be a coincidence, but if anyone is still having problems with the registration form, or receiving a third transfer, then maybe it's not fixed - it's that the two registrations systems are linked and the 2nd works for some unknown reason.
I can't explain any of it, so i'm just going to be thankful that its at least working for now. I hope it is for others too!