The solution to mitigate SIM swapping is the company sending a warning by SMS to the SIM number about the SIM being duplicated so you can take measures in case is not you who is making a duplicate of the SIM.

Edited: Also the bank should send a message to the current number associate with the bank account before allowing it to be changed.

So that the current user of the SIM or account number receives a warning about the SIM being duplicated or the telephone number associated with the account being changed so that he can take the correct measures just in case this is part on an ongoing fraud.