I am facing a similar issue. As far as I know, you should receive a confirmation text which will have a confirmation link. You will not receive until you've confirmed it. But the problem with me is I am not getting a confirmation either. According to documentation:
After you subscribe your endpoint, Amazon SNS sends a subscription confirmation message to the endpoint. The code at the endpoint must retrieve the SubscribeURL from the subscription confirmation message and then either visit the location specified by the SubscribeURL or make it available to you so that you can manually visit the SubscribeURL, for example, using a web browser.