How to make sure if I always have access to my data?
A cloud provider usually should be able to provide an outline of the access, security, services, support and other specifics in a service-level agreement. This agreement details the measures that can be taken in case of any outage (contingency plan).
An example of SLA - aws.amazon.com/ec2/sla/
In order to be confident about data storage, however, it is always better to use multiple services instead of a single provider.