High billing due to upgrade mess-up

I have had a contract with this company for years and for the first time I'm contemplating cancelling everything with them. In April I went to upgrade our phones to a better phone. At the store a young coloured gent helped us to do the upgrades and transfer all our info over to the new phones. I EXPLICITLY told him to put the new phones on our existing plan as I was happy with it and could afford it as my husband is a pensioner. At the end of April I received a huge bill and went back to the store only to find out that the gent had opened our plan and also had left the company. The manager then sent in a report to Autopage head office to have the issues rectified. I May I discovered that the gent also didn't show us or do the correct settings on our phones which also caused major problems with billing and I went back to the store so the manager could help us. Our Bill has now normalised to where it was but I'm being sent from pillar to post and NOTHING is done about this bill. Our phone's are now shut down entirely. No one can get hold of me and I deal with customers daily and I'm also on the road. This is unacceptable.!!!!!!