The reason you are getting different numbers is because when one sms provider fails (for example twilio fails) we'll send from another provider they will be sending from a different number.
If you have a smart phone I would suggest to use Zoho's OneAuth, where you can use multiple options like touchID, TimeBased OTP, QRCode scan or a push notification. This way you can avoid SMS.
In case of SMS alerts the same logic applies. For example, If your sms setting is "twillio" it will be from a particular number. If you set it from "bulksms" it will be from a different number. The numbers will vary based on the your telecom provider.