ACT Fibernet — Raise in Bill and plan

Greetings, On 2nd April I got a bill of 681.00 RS against my Internet usage. However, it used to be 630 Rs previously. On contacting CCare I got to know that they have upgraded plan to 5 MBPS and they sent some message regarding this it seems. Later, after checking my messages, I found that on 25th March 2015 they sent me message regarding upgrade of package from 4 mbps to 5 mbps and increase of cost from 605.00 Rs to 650RS for my plan. Complaint number registered for the same : 16459907 My Beam Account ID : 510893 My Concern is, how can they change the plan with out my written or oral approval. Also, how can they demand me to pay extra. I seriously dosen't need 5 MBPS plan and I dosen't want to pay anything extra... Regards Sanjay.Golla