Yeah, I'd agree with Vlad. You were given a job to create these models for this company and, presumably, were paid for the time you took to make them. Handing over the models along with the images seems like a reasonable request. Then, later on down the road, this company will have the source files available if they need new angles or whatnot.
If you had created the models on your own time and the company was simply paying for the use of renders, that'd be one thing, but if the models were created specifically for this company, then yeah, they belong to them.
If you feel like you're being jipped, you might consider raising your prices for future such projects.