Google Voice now becomes unavailable, any alternatives?

Hello,

I worked for a scheduling company and is using Google Voice to send SMS to more or less 300 people per day.

It was working alright for a year until recently, they kept on blocking the line. The outgoing SMS will intermittently not send anymore. We already contacted GV support but they can't give us resolution.

Do you know other application that can accomodate the usage and can be linked to our company phone number?

Thank you all.