If you were a Patreon a while ago, then it must have been at the time where Gray's chapters 1 through 18 were out. That's the content you paid for, regardless whether Gray is now completely finished. The Patreon model is that you get the content you pledged for, and if you want more content, you'll have to pledge again. Hence why it probably said there's no more content, because this is where you stopped.
If you want to play Gray's route fully, you can play the free version on Itch or Steam, or pledge to the Patreon once more to get Gray's full route and his Plus content, as well as Aiden's full route.
However, if you say Gray's route was finished at the time, you can hand over your e-mail so I can check which month and year you were pledged so I can make sure and sort things out.