Whatsapp for 4 days doesnt take R500(Top Up Cont..

On the 25th of March my account was debited double+ my normal contract rate, I have always paid or being charged more on the contract and will pay cause sometimes my data bundles will be depleted and will only see if I check on *141#. This is a top up contract and I am suprised that on the month of March I was expected to pay R994 whilst my monthly installement is less than R400, after seeing what was debited I did a reversal and called MTN for statement and invoice and the consultant said the extra costs came from data usage but I always switch off mobile data and no one uses my phone but me therefore I need to know how the charges came about cause I was out of data bundles for few days (-4 days). I havent been receiving statements nor invoices ever since getting this contract but would pay as I wasnt suspicious of any irreguralities until the latest bill. Ive tried calling MTN a numerous after the last call but the call Centre is always expereincing high volume calls despite whatever time you call MTN is always experiencing high volumes. I havent received the statement despite the agreement with the last consultant therefore need to know how they got to R994