Is it normal for a developer to go the customers to troubleshoot a certain problem?

I mean, we got technicians & support department

Depends on the company but normally not.

If you sell software on premise some calls are unavoidable.

@Lensflare should be right in the whole world, but depending on where the company is, developers are considered "computer kids" and all "computer stuff" falls on them.
Including machinery like the A/C and microwave oven.
When I was a wee lad, I was asked to travel 300Km to install an app in the client's systems. Our company's app was a *website*. They were asking me to install a website. Because it was their company's policy to have their vendors install every system purchased.
Never underestimate the amateurism of company managers, especially regarding departments they are proud to know nothing about.