MTN Incorrect data billing

I've had my 3g wireless router with MTN for two years and I never go over my 2 gigs per month - so I pay my R159 per month and I was happy with the service. In January we opened a new office and our IT wasn't installed in time so I was using my 3g wireless router to access the internet - it was myself, my colleague and sometimes I gave clients access. <br> We worked like this for three months and I was charged accordingly. The company i work for has several web based platforms for the various tasks we do on a daily basis.<br> My Packet switch data was charged from 7am - 17:30 Monday to Friday<br> January R325.01<br> February R1391.02<br> March R911.01 <br> In April our wifi / fiber connection was installed so i took my 3g home and only used it in the morning from 5-7am for whatsapp etc and at night from 4:30 to 9pm for browsing.<br> My packet swith data charged :<br> April R1721.80<br> May R3688.31 <br> How is that possible? I looked at my itemised billing and according to the statement I download every 3-5 minutes through out the night. Nothing has changed since Nov, Dec last year when i was paying my R159 p/m. I logged a query and they say the billing is correct. I'm sick of MTN ripping my off. Not the first time!!