MTN is dissapointing

l have been paying sending the proof of payments monthly until MTN invoiced me twice and and they say that l did not pay for the month of November l sent them the proof of payment and still they don't respond on time l complained that l lost my phone l pay insurance and they did not respond to me , l sent then an email and l stopped paying as they are not helping me now they say l owe R36000 which doesn't make sense ,l stopped paying recently when l lost my phones and they refused to help me. l have paid them R20000 so far l have all the proof of payments.