Cannot change VMLite to standard voice mail

When I changed from Contract to pay-as-you-go then my voicemail changed to VMLite, which means that you cannot set a message for callers and also callers cannot leave a message for you, MTN just sends me a SMS giving the caller's phone number. I have been to the MTN branches to try and get my voicemail changed from VMLite back to normal voicemail without success. They reset my voicemail and I record a voicemail message. I then get a SMS saying \congratulations you have successfully set up your voicemail". I then ask the \""consultant\"" to call me and test my voicemail. She calls me and the message she gets is \""Welcome to MTN voicemail lite. You need not leave a message as MTN will send your number to the recipient\"". It does not change to standard voicemail. Please assist."""