Soft block

I app**** for a 2Gig top up contract for myself and a 1gig top up for my fiance's number everything was good after I received a call about a month ago from someone from Vodacom the guy explained that we can still be on the same contract but now for only R99 pm so I agreed on to continue with the contract.Two weeks later when we want to top up the data we couldn't as all of a sudden we are on a 2GB open plan package whitch I did not apply for or was aware of when I phoned the call centre ... Now I owe vodacom more that R6000 on the two numbers and now they put a soft lock on the numbers so we can't do anything using the numbers we have been to a Vodacom shop and they switched it on 2 hours later its off again the next day I phoned them and the same problem. They keep switching us off and no one can answer us by saying where the problem is ...we never use more than 4gigs a month and why will they just switch us to an open line??? I refuse to pay the money as its not our fault...its been now more than a week with this problem I have to phone customer care to switch it back on and a few hours later its off again so we cac't receive any incoming calles aswel... We have been with Vodacom for over 10 years and now we have this problem???