Poor service by MTN

I took a cellphone contract with MTN in 2012 and every 24 months I was renewing my contract with them. The last renewal I made was in 2017 for another 24 months but now to my surprise they told me that I took a 36 months contract with them and that my contract is ending only in 2020. I've sent numerous emails to them to show me the proof but till today they've failed to furnish me with that. I mean who in their right mind takes a cellphone contract for 3 years. Poor service is all I can say.