CANNOT FIX A SIMPLE ERROR

I previously had a contract with Nashua Mobile. I was advised towards end 2014 that I had been switched to MTN (with no prior notice). During March 2015 I confirmed with the MTN store in Nelspruit that my contract expires at end March ( the monthly payment on this was R699 per month). I requested to change the package to a data package with a Note 10.1. and 2 gigs of data at R349 per month. On 4th April I received a call that the tablet was available. We went the same day and signed for the upgrade and confirmed that the new monthly amount would be R349. (I have documents to prove this). In April I received a bill for around R850, and paid without querying, however in May I was told I owe over R1000. I phoned in with a query and was told it would be investigated and I would get feedback (I still wait, and I have a query reference). Thereafter we received periodic warnings and threats, the problem was they were also on strike so you could not contact anybody. I even tried the switchboard, but got nobody to assist. Finally today I get a call from the collections dept. at around 10h00 I tell my story, only to get an arrears sms at 14h37. ENOUGH NOW, I WILL TAKE ACTION IF NOT SORTED!!!