4 Years later and my number re-issued to someone??

I just received a message saying \Congrats your SIM card was successfully RICA'd. Your new VM number is #####"Let's start off by saying I ported 4 years ago!!!! I then called the call centre and spoke to Rebecca and she confirmed with your technical department that my number has indeed been RECYCLED and someone got their hands on it via a prepaid pack. Firstly HOW is this possible??? Secondly everything is linked to my number does this mean my smses will be going to whoever bought this starter pack??? I don't have to tell you that this is a major security risk and if any ***** has to happen as a result"