Harrasment for expired contract.

I took out a contract with 8ta in 2011 .the terms were for 24months.when I wanted to extend the contract after 24 months I was told that there is no further contract and it would be a month to month basis until I no longer made payment and wanted it to end ,the service would end. I stopped payment in 2016 with the understanding that the services offered by 8ta would cease to operate. I have now been phoned by attorneys informing me that I have broken my contract and now need to make a payment of R3500 . Please advise me urgently what cancelation fees these are considering I have no contract??