Personal details sent to someone else

I have had a very weird experience where no-one seems to be able to tell me what happened or how my problem is going to be rectified. Someone I know had their phone ******, so I offered to use my talking points to get a new phone for them while we were on a business trip. The phone came brand new out them box and they put a telkom dim card in. I never used or handled the phone. Now they have called me to tell me they suddenly have all these old smses on their phone almost a week later that came overnight. Some were forwarded to me and these are all my old message. This include all my bank balances, personal sides as well as sensitive business information that they are not privy to as a junior of mine. I am now nowhere near them and have no way of ensuring this does not get into their hands. How did this happen! The call centre tells me it's impossible, but I have the messages to prove it did happen. I need this reversed and ASAP. I have no backup accounts that could have reached this phone as it was never in my possession. Vodacom you really need to sort my problem out here.