MTN contract breach

We have a MTN Made to share business account with simcards linked to the account.

The application that we used to manage the accounts was taken down by mtn and now there is no way to manage the business simcards or set date usages.

No one at mtn can assist us. Customer care said contact the account manager. The account manager said to contact customer care and that the developers are aware of the situation (this has been going on for more than 2 months now).... We have a contract but MTN is in breach of the contract. We have mailed everyone possible with no reply. They have no problem taking our money every month, but don’t care if we lose money due to the service not working. What now?