Contract upgraded prematurely

I have opened an router account for monthly 10 gigs in 2017 January and the contract was 24 months. But for some reason that the account was upgraded prematurely and it was in 2018 January for 20 gigs with another 24 months. I have noticed this after 8 months that my contract was upgraded and at the time I was behind with my payments so didn't managed to get the answers .