UNKNOWN CHARGES

I am a pensioner who have 2 Accounts Routers which I am supposed to pay R280 monthly for. I have been paying this amount until January this year where without explanation the amount went up. I use only the Routers and do not even use it to call. I want to know how these routers are on contract can suddenly go up and no one is able to tell me why and how. Clear this because it is getting out of hand