It’s strange that such a solution didn’t occur to you, because my first step would also be going to the service center or back to the store where I bought my iPhone. Either way, do that. If anything, you can try different tips and solutions from here https://setapp.com/how-to/how-to-fix-cellular-data-not-working-on-iphone-ipad. These kinds of articles can be really helpful sometimes. Some tips may seem pretty basic and obvious, but you wouldn’t believe how many times I’ve used them and solved the problem.