Cancelation and increasing of the amount not letting us know

Web Africa is the worsed internet provider they said when applying for the internet wifi we will pay month to month 400 a month when they debit money but recently they debited 600 last month and when contacting them they said we are unable to cancel the wifi we on a contract that when I apply I know that it's a month to month payment of 400 a month and it saddenly changed to 600 a month not knowing that but I want to cancel my subscription with them and look for a better deal with other service provider.