Sim swap via online at Cell C call centre

Yesterday being the 31st of january 2020, my cell phone was hacked .Cell C did not send any type of message to say that a sim swap was requested or done on my cell phone . The only sms I recieved was to say that my line was deactived. Upon inquiry via the number that was provided I learned that a sim swap was already done. I notiified my bank and was told that Airtime had been purched already . I went of th Cell C at Carnival mall and had to do a sim swap again for which I was charged R115.00. I inquired about how this transaction was done and was told it was don on-line via the customer care centre. How can it be possible that someone can do this over the phone when eveytime you go to a centre you need to produce your id. I was charged R150.00 each at the bank for having to get new cards (debit and Credit card) as they had to block my account and cancel my cards. Banks depend on us to give them a cell number for notificatios but the cell phone companies just let this type of thing happen . Yesterday been the end of the month my debit orders have now been compremised due to the account been blocked . Cell c seem to have the position of "It's not my problem".Please help.