I'm so disappointed with mtn

I have month month contract with mtn since the 25th on February which i paid, yesterday my contract was suspended and they told me that i have to pay on the 4th of every month. and the sales consultant i agreed with him to pay on the 25th of every month. now they want me to pay twice in a month which i have already paid. i tried to explain with them but they are forcing me to pay. how can i pay for twice in a month?