“God never said He would be a God to Ishmael.”
He did to Abraham. Muslims say they worship the God of Abraham.
“He said He would be a God to Isaac.”
And Abraham before him. Muslims say they worship the God of Abraham.
“serve the God of Abraham, Isaac, and Jacob. I do not serve the same god as the Muslims.”
So the God of Abraham is not the God of Abraham - that’s what you’re saying.
Far be it from me to stop you from believing in the same god as the Muslims.