Development of MVP

Startup is looking for freelancers with experience working with broadcast calling systems and services, e.g. text-em-all, dialmycalls, ringcentral. We want to develop a system that send calls to our customers when a event is triggered. We dont know what language, framework, or database to use, we are open to suggestions. About the architecture we want to deploy it on lambda services, and it should be microservice oriented. We do not want to have only one call provider, we should be able to switch or change it according to the market situation. More details will be provided during the interview