FNB UNFAIR PRACTICE

FNB has blocked my account and are not listening to me when I tell them that I am not a signatory nor am I involved ore are registered in my son's business or finances .My son has both a business and personal account with them and at some point when he lost his phone he used my number to get in contact notifications from the bank and later changed it to his number .i woke up two days ago to my surprise my bank account was inactive and money was deducted from my account when I went to inquire at Mookgophong FNB branch they could not get hold of the relevant department and ended up emailing them.My question is how does FNB make me pay my son's debt by force?and from the response I had from FNB it is clear that they never took time to investigate the matter I really need help and to be refunded