No one seems to know what the problem is!!!!

I bought a Tablet on 22 January 2015 which calling capabilities and on 23 January 2015 did a sim swop at my local Vodacom shop. Since the sim swop I have not been able to received any calls. When someone calls my number it gives them an engaged tone and all I receive is a notification of a missed call. I can make calls, no problem. I contacted the call centre and the consultants were very friendly and helpful but the problem was not solved. This was done numerous times...with no satisfaction. I finally went to the Vodacom shop at Canal walk on Monday, thinking that having the device in front of them, will make it easier....after about an hour I left as the consultant was once again unsuccessful. Got a missed call from Vodacom today and I call them back...to be on hold for about 5 minutes and told that they did not call me. I have been very patient and its almost 2 weeks now that they have not been able to solve this issue. PLEASE CALL ME on my work number as you should have it!!!!