Billed Pensioner Ridiculous amount

My father is a pensioner&was charged an amount R6000 in september to have his account unsuspended. It started with an amount of R2000 every time we called to have lines unlocked there was another 'hidden' amount that escalated.MTN head office was contacted&they advised that this was an amount running for 2years!How can MTN have let this acc run so high, if you are outstanding on an acc it gets locked the next month not in 2years time?A brief acc was sent to me&another concern was raised 1 of the Nr. is a top up acc and the bill varies each month, surely this should be a fixed line!This acc was paid Only to have the lines unlock we still do not understand how this is remotely possible?Is MTN in such a mess that they are now trying to point the blame on clients!!!