I had this whole reply written out and then realized how asinine your question actually is.
Let's say (for the sake of ease) you owe them 100 a month (1200 annually)
You should pay 12 payments of 100 dollars.
Instead, you make 20 payments of $60, or 1.6 payments a month to them.
This does not matter to them, nor will it affect them in any way as long as you pay the full bill on time.
*This also largely ignores the contract you signed (you read it, didn't you?) that clearly states what your responsibility is and what theirs is. I'm not saying they're right, I'm saying you went in with fully knowledge of what the situation was and did it anyway. you could have walked away and picked a different carrier, signing a contract in your own free will and then complaining about it is beyond ridiculous, no one made you do it.