Impossible to cancel Webafrica 6 months down the line

As a business we signed up with Webafrica for our space. We have since closed our space and have been trying to cancel the internet service since November 23 and they are still deducting the premium every month and have also billed us for the router, which they should have collected on cancellation. then we discovered that they have also double deducted one of the directors private internet from her and from the business every month since she joined Webafrica. We are at a loss and desperate to find a way to stop their deduction because they are relentless and nobody even up to senior management has been able to assist us.