MTN ******** SIM swap

I have just noticed that my phone was not registered on the network and when I went into MTN I was advised that an ******* SIM swap has taken place. I did get an SMS whilst on vacation was due to no signal could not respond. How did this sim swap still happen?

I would be interested in laying ******** charges against MTN as I believe this is in breach of data protection laws. ANy one with suggestions?