Well, as the mobile verification is subject to a fee of 1 Credit, therefore, you will need to have a minimum of 200.99 Credits in your account to verify your mobile; since the first 199.99 Credits are reserved by the RRS at all times; for your next upgrade.
If you do have enough Credits in your account, but you are somehow not receiving the SMS verification code, we suggest you contact your service provider to see if they might have blocked you from receiving these text messages.