Similar happened to me earlier this week.

Give it a day or so and see if they allocate you another flight in MMB. You’ll get a text with a link asking if you want to accept that, or if nothing allocated to ask them to book you on the next available flight, or take a refund.

In my case no flight options were offered and I didn’t want to wait for them to pick another flight for me so I needed to phone them. Couldn’t even get in the queue on the number provided but did manage it through the Blue exec club number in the middle of the day after about 30 mins. Changed flight to the day before and car hire updated to match.

Very frustrating but a bit of patience and persistence sorted it out.