My company would rather hire someone new than give me more work… should I be worried?

I've been in my current role for 11 months and I'm increasingly running out of work. I regularly have around 5 hours of spare capacity.

I've asked my manager for more work and she is trying to find things for me, but I’m starting to wonder where my role is actually heading.

When customer service was previously understaffed, I was put on calls to help out. In one particular month, I handled around 590 calls, and I have 9 years of customer-service experience. I also genuinely enjoy customer service and told my manager I'd be happy to continue supporting the team when I had spare capacity. However, I was taken off calls because she wanted customer service to focus purely on customer-service work.

Now I've found out she's hiring another customer-service person, despite knowing I have significant spare capacity and already have the experience. This will be the 4th customer-service hire since I started, as the previous 3 haven't stayed. My manager says she wants someone committed.

I'm planning to ask her tomorrow how she sees my role developing and whether there's anything in the pipeline to give me more responsibility.

Am I overthinking this, or should be concerned about the future of my role?