Outrages billing!

I took out a 3Gig data contract with a device for R199 per month in 13 February 2015. Migrated to a 5 gig on 20 May 2015. The billing is just totally incorrect! R394 was deducted from my account on 5 April for February (pro-rata) and March. Included in this was R99 for calls (on a DATA-ONLY DEVICE!!!) On the 6th May R199 was deducted for April (which is correct). On the 6th June R199 was paid for May which is also correct. Then I migrated to a 5Gig package and from thereon the nonsense started. R713.85 bill in June for a package that is supposed to cost R289! After phoning and asking for it to be corrected, they deducted R578.83 from my account on the 7th of July! Now a bill for July of R764.70 for the same R289 service. When will you stop with this **************** and get your accounts in order! The people at my local branch can't even help me and I have to call customer service myself!