I've got my pre-order in with Argos, thanks to @Bojan11 alerting me and have cancelled the ShopTo after they did the same thing to me as you. Still not sure whether to go in with someone else, especially so since Argos take the money in advance. ShopTo are wishy-washy in my experience - a proper 50/50 so I'm not surprised they've done this.I'm assuming their allocation of day one units was way smaller than they thought it would be. I only went with them because I had a decent experience getting a PS5 day one.
Not too fussed about day one really, but it'd be nice to have it sometime in June/early July.
Argos have always been rock solid with this stuff once an order is in, but I've found John Lewis and Very to be the gold standard as they make you a priority no matter what and even deliver early. The former haven't even started their item page and Very's stock is very much be first at an alert, but yeah, if you don't mind when yours arrives it make sense to go with your most trusted retailer. Mine is very much time dependant, so don't want to take any risks with it.