Paying double with upgrade

Telkom mobile - people be careful when you upgrade for the 1st time, they charge you the prev months bill + handset as well as pro-rata on the next 2 months, when the said there will be pro-rata they didnt explain that you will loose your old paid data and recharge you for new data and charge you for your handset prev and new in 1 bill R1200 more on my bill... Really thought I made a beter move to telkom but never had to pay anything like this with vodacom