Congratulations on your first job! Your payday seems to be just like a gold mine for you. But after you find out how fast your pay will be eaten by all your bills, you will understand that negotiation might help you a lot, and you can save a lot of money. Companies expect you to negotiate, so there is nothing to be afraid of.
First of all, call your provider directly. Ask for the retention department, as they are the only ones who can give you something extra. Mention the possibility of leaving the company as your primary reason for such a step. It usually works perfectly well and helps to get some special offers.
Refuse their first proposal. If they reduce the cost of your internet package by ten dollars, you should ask them to reduce it for twenty dollars. Every company has a minimum cost, but you are not aware of it. Negotiate until they go to the bottom.
Mention the fact that you have seen some interesting offer from other companies, such as T-Mobile or Verizon. Say that you would like to have the same deal as new customers due to your loyalty. They will surely refuse, but tell them to ask their manager about this request.
Stay polite but firm, as it is really important for you. Losing your temper will have the opposite effect.