R345 because of cancelled contract

I m fed up with Cellc, end of Feb 15 I cancelled my contract and I have enough data and minutes still available on contract, it was all taken away. I queried why I was told because I migrated to straight up all my data and minuted i forfeit so i thought ok when r you loading my data, I was told it will be loaded the next day. The straight up contract of R110 was loaded and i received sms to confirm that but my phone was loaded with 6.45MB data. Now end of April I cancel straight up contract because when u want to add data you are not given all you data it is loaded proportionally depending on the day you called call center to buy extra data(don't make sense as why load another portion of data when you reload data). On Monday 3/5/15 I contacted call center to cancel my contract and I was later send bill that I owe R345 on inquiring I am told that its because smart phone used data at the end of my contract amounting to R145 until the new contract kicked in. Funny how such lame excuses are now been used to ****** money from customer and why now at end of my contract such data is used by my phone conveniently after i have cancelled my contract. THIS IS DONE INTENTIONALLY TO BLACKLIST