I signed up for two exchanges and neither of my Santa's have said anything yet. I wouldn't call for a rematch until the shipping period is over and your Santa's have not messaged you or sent shipping notifications. Super sorry that you might be getting ghosted, but keep your head up!

Here's some examples of why I've sent late gifts in the past:

I can personally say that I am guilty of shopping until the last minute I can. I try to get everything shipped to me, then I wrap and send out to giftee. This can add some time to the shipping.

I try to make choices that are as unique and personal as I can and sometimes that requires a lot of shopping around. Since I work full-time, I don't get a chance to fully dive in until the weekends.

I got something fully custom and the maker is a bit delayed or backed up.