Bad Service

I took out a uncapped home internet with MTN, then the sales agent told me I can use the sim with any router of my choice, so when I got sim i inserted in the router it didn't connect, when I inserted in my phone didn't work so I called MTN and they told me that my contract is under Mondo and I was never told from the word go, then I called mondo then mondo told me to call mtn they will help me, I did those steps repeatedly still even today the sim is of no use, but they keep sending bills saying I owe them and the prices keeps going up for monthly fees while I have never touched the data