I don't have any advice for you but wanted to say that we are in the same boat. 3 yo dd was fully trained then we moved in November and over Christmas she has fully regressed with wees. Sometimes she hasn't even finished saying she needs a wee before she has wet herself, sometimes she just leaks a bit in her pants.
We too got cross and threatened to put her back in nappies which made her sad and us feel terrible. Apparently regression is very common for pre-schoolers when they have a lot going on. I have reinstated the potty chart and am having about a 50 percent success rate with that, and am trying not to make a big deal out of accidents (easier said then done!).
Toilet trained both DCs (DS 3.9 and DD 2.6) at start of summer holidays. It was all going well except DS wouldn't poo in toilet. He kept saying he didn't know he had to go. Things got slightly better though.
We moved in October and things were lots better with DS but in the last month or so both of them keep wetting and soiling themselves. I remind them to go to the toilet but it doesn't make a bit of a difference.
I have no idea what to do. Do I go back to the start and make them sit on the toilet every hour or so? Or just put up with it and hope they go back to how they were?
I lost it with DS earlier and told him if he didn't start pooing on the toilet again he wouldn't be able to go to school when his friends do so now I feel guilty about that.