Since yesterday, the messages have completely stopped coming so you might have reached the SNS SMS spend limit for your account. By default it is 1 USD for a AWS account in a AWS region. You can check Delivery Status logs which might say 'No Quota Left for Account'.You should get your limit increased with limit increase team for which you do not have to pay 29 dollars.
But in future if you want to prevent this i.e. if you want to get notified earlier before you reach the actual SMS Spend Limit for your account so that limit can be increased before hand. In this way you would not face SMS delivery issues due to limit being reached. You can create a CloudWatch Alarm on your SMSMonthToDateSpentUSD metric.
Please have a look at this video: https://www.youtube.com/watch?v=5-HdLf_lizI

Since yesterday, the messages have completely stopped coming so you might have reached the SNS SMS spend limit for your account. By default it is 1 USD for a AWS account in a AWS region. You should get your limit increased.
But in future if you want to prevent this i.e. if you want to get notified earlier before you reach the actual SMS Spend Limit for your account so that limit can be increased before hand. In this way you would not face SMS delivery issues due to limit being reached. You can create a CloudWatch Alarm on your SMSMonthToDateSpentUSD metric.
Please have a look at this video: https://www.youtube.com/watch?v=5-HdLf_lizI