Just cancel the subscription

i had a sum only contract with man which came to end in november.mtn tried to give me offeres which i did not accept..am agent called me and advise that i will be on a month to month plan and that the premium is still the same.in november and December i have financial difficulties and did not pay..service was discontinued which makes sense..to my surprise now i receive an email that i owe man R1200, how? Yes i did not make 2 payment s and no data was given to me, and my premium was R208...please just canceled the subscription am done with you