Locate the "Sitecore.Cloud.ApplicationInsights.config" in your \App-Config\Include\zzz folder, and disable it by adding ".disabled" to the end of the filename.
In your "ConnectionString.config" file found in \App_Config, remove the connection string for the AI instrumentation.
<add name="appinsights.instrumentationkey"
connectionString="XXXXXXXXXXXXXXXXXXXXXXXXXXX" />
In your \web.config file, comment out the following entries:
<httpModules>
<add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" />
<dependentAssembly>
<assemblyIdentity name="Microsoft.ApplicationInsights" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-2.3.0.0" newVersion="2.3.0.0" />
<system.diagnostics>
<trace autoflush="true" indentsize="0">
<listeners>
<add name="myAppInsightsListener" type="Microsoft.ApplicationInsights.TraceListener.ApplicationInsightsTraceListener, Microsoft.ApplicationInsights.TraceListener" />
</listeners>
</trace>
Perform these steps on the following server roles: CM, CD
Finally Delete the Application Insight Service in Azure to stop billing. :)
For more information read this :
http://integryx.net/post/2018/05/19/sitecore-9-paas-disable-application-insights