Test classes not running in parallel in selenium

I am trying to run test classes in parallel in selenium .Chrome Instance creates for 3 times suppose i have given thread count 3 but only one instance is working rest of instance is not working.Can anyone help me out to solve the issue.

I have created testng.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite thread-count="4" name="OETestCase" parallel="classes">
    <listeners>
        <listener
            class-name="com.dev2qa.example.testng.report.CustomTestNGReporter" />
    </listeners>
    <test name="AllOE testCase">
        <classes>
            <class name="SRS_ECOM_SMOKE_INT.Allison_ECom_Test" />
            <class name="SRS_ECOM_SMOKE_INT.Audi_Ecom_Test" />
            <class name="SRS_ECOM_SMOKE_INT.DA_ECom_Test" />
            <class name="SRS_ECOM_SMOKE_INT.Polaris_Ecom_Test" />
            <class name="SRS_ECOM_SMOKE_INT.Scoda_Ecom_Test" />
            <class name="SRS_ECOM_SMOKE_INT.Subaru_Ecom_Test" />

        </classes>
    </test>

</suite>