I am so sorry for your loss.  It sounds as if your Grandfather was a wonder man and took on the responsibility of raising and supporting you seriously.  If he did not formally adopt you as a child and he died with out a Will (called "intestate") then you would still be considered a grandchild under the law and not a child.  His actions during his lifetime - although commendable - are not enough to raise your status from a grandchild to a child under the law.  Only a formal adotion could do that.  However, what I do not understand here is why he paid child support for you.  That is an issue that you need to explore with an attorney in your area.  If there was an order establishing you as a child and not a grandchild that may be enough here to raise your status.  Please seek legal help.  Good luck.