My numbers assigned to someone else

Today I went to menlyn shopping center to do a sim swap due to by sim is broken, I had that sim card since 2008 till now...almost 12 years using this number and they tell me that it was assigned to someone else (O_O) Now I cant get my numbers back? Please fix this system of your becouse it's wrong....I am using those numbers everywhere WhatsApp Facebook Emails and everything else How is it assigned to someone else it means vodacom