Is it true that the credit card received an ultimatum from a private mobile phone message after the deadline, or is it a reminder from the dunner?

If it is overdue for a long time, any information you receive has nothing to do with the public security government and other institutions temporarily. It's from a private debt collection company subcontracted by the bank, but if you still don't pay it back and the amount owed is large, the bank will consider reporting it to the local police station. Once the police station decides to file a case, such an institution will naturally look for you.