It looks like the pageNumber field of the GET/api/v2/outbound/callabletimesets API is ignored when using the javascript-sdk getOutboundCallabletimesets() function.
I have 3 callable time sets configured, all show up on page number 1. If I ask for page 2, the same callable time sets appear. Same for page 3 and so on...
Since the behavior is the same with the dev tools and the SDK, it sounds like an issue with the backend service. Please open a case with PureCloud Care to investigate further.