Vodacom number "missing" and bad service

I was a customer at Vodacom since my very first phone (At least 13 years). Had the same number from the start. That was until last year. I went to work on a farm near Britstown in the Northern Cape. On the farm there was NO Vodacom reception. I had to buy an MTN sim card as MTN had full coverage there. That is not the problem. Vodacom then stopped the number as I did not use it for longer than 6 months. Still THAT was not the problem. I came to Gauteng for business and went to Vodaworld in Midrand to see if I can get my number back as all my family and friends and other business contacts has the Vodacom number. The PROBLEM happened that when I wanted my old number back the lady that assisted me said that that number never belonged to me. She refused to give me the name of who she said the number belonged to or help me in any way. Now I was a contract customer for at least 10 years before I switched to prepaid on the same number. I received statements every month for that number. sometimes for the amount of R11 000 (I worked overseas. My question is how on earth did my number suddenly belonged to someone else after all that time? The number is/was ***.