Harrassment of a non customer

Last week Friday alone I received the following message 9 times between 4:30 and 17:30 "Nedbank: A notification has come through for this number. These details do not match Nedbank's records. Please visit a Nedbank branch to update your details". In the past when I was being harassed with this message (have recieved it up to 15 times in one day) I went into a branch but they were very confused as I do not have a Nedbank account. The closest contact I have with Nedbank is that my boss is with Nedbank but she knows nothing about these messages and they do not tie in with pay day. I get these messages for a few days then it goes quiet for a week or a month or two and then suddenly I will get an influx all in one day again. I have rep**** stop and opt out but it makes no difference. I have had the same cellphone number for about 20 years so it is not a case of my number having been someone else's number that I have taken over. PLEASE HELP!!!!!!