Cancellation of contract

I phoned and mailed a cancellation request for our business account on 28/02/2020 to cancel our contract on 31/03/2020. I received a call mid March to confirm and that they will cancel it 31/03/2020 and collect the PABX system the same day. Before then the lock down started & I keep receiving new invoices every month. I mailed them 3 times after that to confirm cancellation & to arrange for PABX to be collected. When you phone the call center they just say I must wait for them to phone us. I received a new statement again & they keep billing us. Since the lock down we aren't even in our office as every one is working from home. They keep billing us for rent and I don't receive any feedback on the cancellation.