Consider what you are saying here. You are willing to accept that there can be such a thing as an "illusion" as a premise for your question. However, you're not convinced that there can be thought.
An "illusion" is an instance of a misapprehended perception of some sensory input, so in order to use this concept of an illusion, you have already accepted (as a premise to your question) that we have senses, we have perceptions of sensory inputs, we have apprehensions of those sensory inputs, and there is a possibility of mis-apprehension of those sensory inputs. In short, you have already accepted that we have sensory inputs and then we think about them, and our conclusions about these sensory inputs can be compared to some objective external reality to determine if they are correct apprehensions, or merely "illusions". When you use the concept of an "illusion" in your argument you have already accepted all of these preliminary positions; even by using this concept of "illusion" you have already accepted that we're thinking. (Or to put it another way, if there were no thought, there could not be a valid concept of "illusion".)
This kind of attempt to deny the existence of thinking is an example of the "stolen concept fallacy". It is not possible to deny the existence of consciousness and thought, without invoking concepts that logically depend on the existence of these things. Any argument against thought must involve the use of concepts that pre-suppose thinking. For this reason, the existence of thought is an axiom --- a concept that is necessarily taken as a premise to all other observations and arguments.