Adding an annotation to a class using Javassist

I am trying to add annotation to class dynamically using javassist

My code as follows

private Class addFrequencyAnnotation(String className,String annotationName, int frequency) throws Exception{
    ClassPool pool = ClassPool.getDefault();
    CtClass ctClass = pool.makeClass(className);

    ClassFile classFile = ctClass.getClassFile();
    ConstPool constpool = classFile.getConstPool();

    AnnotationsAttribute annotationsAttribute = new AnnotationsAttribute(constpool, AnnotationsAttribute.visibleTag);
    Annotation annotation = new Annotation(annotationName, constpool);
    annotation.addMemberValue("frequency", new IntegerMemberValue(classFile.getConstPool(), frequency));
    annotationsAttribute.setAnnotation(annotation);

    ctClass.getClassFile().addAttribute(annotationsAttribute);

    return ctClass.toClass();
  }

But the class returned does not have annotation added. I am not sure what is missing in my code. Could someone help to identify the issue?