MTN Billing Fault

A few years back I had a contract whereby R200 was allocated monthly for airtime. I used to roam in Namibia using the phone frequently and then the roaming charges were deducted from the airtime available on the account. In the event of depletion no outgoing calls were allowed any further. I also came to realize after my almost R400 worth of airtime disappeared that when the incoming call go over to voicemail I was still billed against the available airtime. Recently with a similar contract which had over R300 worth of airtime available on the account and made calls in Namibia under the impression it will again be deducted from the available airtime but this time I received a separate bill close to R700 for calls made. I was told by MTN that calls were always billed separately when roaming which was not the case previously. I have personal experience and logged a complaint previously on this platform with regards to that dated 31 August 2015. They rep**** on the 15th of September 2015 and stated that the roaming caused the airtime to be depleted and this proves my statement that things used to be different and changed in the meantime.