You say that you suffer from severe depression. As you probably know social isolation and withdrawal are symptoms of depression, and treatment involves actively forcing yourself to engage with other people, engage in activities, and basically stay involved in life. You may not feel like doing this (because of your depression), but again, treatment for depression encourages social interaction.
You also say that you do have a few family members who you contact sometimes. Can you pick one or two of these relatives, to connect with more strongly? This would mean making the effort to contact them each day. Maybe even tell them that your counselor has encouraged this to help improve your mood. You say that they don’t contact you unless you call them, so perhaps you can ask the one or two special relatives who you choose, to call you daily.
It’s important for you to live life actively. Do you have a hobby, an interest, or a cause that you can become more involved in? Can you take a class, join a club, a sport, or do volunteer work? Can you schedule one thing each day that gets you out of the house and involved in a meaningful activity? Is there a support group for people with depression that you can join?
If you fear dying and nobody knowing about it, then a practical solution to this is to maintain human connections, as suggested above. But it will take conscious effort, as you push through the downward pull of depression. Please try. Your cat will thank you for it!