Website not loading for some people. What should I do?

I own a website https://ministryofcleaning.com.au My wordpress based website is not loading for some users, while it works absolutely fine for me and many other users. My developers says there is no issue with coding, what should I do?

I have upgraded to latest wordpress & php version. Website loads perfectly for me, loads fine on my friend's mobile as well. I am getting visitors, but then some people & random telemarketers have said my website is not working.