With my advice I am presuming that DS has no additional needs that would account for his egocentric behaviour. For example a child on the autistic spectrum would struggle to take others feelings into account and so behaviour which you describe would be somewhat expected.
As other posters suggested! It sounds like he needs to be retrained in regards to what is expected of him. It won't be easy, and you will have to bare the brunt of his confusion/anger for a short while, but once he becomes used to the new way, your lives will be much easier, and more pleasant.
I'd start by taking away privileges, which can be earned back for a limited time at an agreed time. By privileges I mean screen time, treats including pocket money, sweets etc, trips out, and the like. These things are not rights, as his parent you are giving him everything he needs to thrive as long as he is fed well, sheltered, clothed and loved. Leave him with a few bits to occupy himself that are constant eg books, lego is as good one as he can use it on many levels, paper/pens etc. These are things that he has control over, when to use etc.
Give him responsibility. At 7 he should be able to get himself up, washed and dressed, make his bed, sort his clothes for the wash, keep his room tidy etc. he can also help you out, sorting, putting away laundry, setting the table etc. you'd be the best judge of what his caperbilities are, but encouraging him to participate in the upkeep and running of the house makes him understand his value as a member of the family team rather than someone who is waited on, and therefore more valuable than the person doing the jobs. If he is doing what you ask the pocket money (if that is what you do) can come back. I read a book, can't remember the name, where the author suggested having three money boxes, which pocket money got split between. One was for spending, to help the child learn to budget, one was for savings, to help them appreciate how money can accumulate and give them something towards their future and the third was for charity, to give the child a sense of doing good for others, that other people's needs matter too, it might help give your son some compassion for others. He could choose a charity which might involve him researching into other's difficulties and give him some perspective and compassion.
Things like screan time, and other treats can be earned by completing homework, reading etc and by being respectful to the other members of the family etc. They only happen once the above have been completed, but let him know in advance, to encourage him to engage in these things on his own terms. By doing this you will give him the responsibility which is a life long skill and will give yourself an easier time because you won't need to nag him to do it. If he asks you can I go on the tablet or whatever, simply say yes, of course, once you have done your reading or homework or whatever it may be that day. Then let it only be for a given period of time 1/2 would be pleanty for a 7 year old but you know yoyr son and will make the best decision. The danger of going over an hour is that the gratification is reduced and the need to play is more addictive rather than enjoyable.
If he complains when it is time to end the 'reward' activity ask him if he behaves like that when using x is it more or less likely to make you want you let him use it again. It will actively encourage him to see the way he behaves had a direct influence on others.
Finally as hard as it may seem at first, and as tired as you may be some days and want to give in for an easy life, you MUST remain consistent. Being firm but fair gives him a sense of safety, knowing exactly where he stands. He will push against you, especially at first, because that is a natural instinct, but when children's boundaries are flexible they often end up angry and insecure because they don't know where they stand and it all can get bit Lord of the Flies!
Hope it helps, it gets easier I promise 