Network Problem in Note 9

Hello there, I am using Note 9 and i am having network issues in my hand set frequency is low  can't use internet properly area networking systems is good bcoz i am having problem only in my note 9 at service center they do software in my phone and say that it will ok now but its still stuck sry for  review but i think Samsung handsets are dropping down bcoz of there network issues kindly fix that problem i love to use Samsung handset but this may change my mind next time so give me a solution for my phone. As soon as possible🙏