Unable to transfer my fund to new company - why are there tax implications to transfer!

It has been trying for 3 months to get my provident fund transferred from Old Mutual to my new company's fund. Their lack of communication has just made this process appalling. Firstly, they do not respond to your emails with the information you actually need. It is just a automated/same response every time. 2) For the life of me, I do not understand how a transfer without withdrawal has tax implications 3) I am still waiting for an email from the consultant who assisted me to start the transfer process. Can someone competent please assist!