Ok yep they would be the ants that farm aphids. Depending on how you feel about chemical use and pesticides there are a handful of items on the market that will take care of this issue. My go to chemical lately has been Bayer 3 in 1 (with mitecide).
https://www.bioadvanced.com/products/rose-flower-care/3-1-insect-disease-mite-control Its strong and kills most problems on the first application. It will also kill honey bees so only spray late in the evening when the bees are back in their hives for the night.
A less aggressive approach could be something like safer soap.
https://www.saferbrand.com/safer-brand-insect-killing-soap-concentrate-16-oz-5118-6 A much more forgiving product on your local bee population but may require multiple applications to finish the job. Also like I mentioned before, a strong jet blast from the water hose will take care of alot of insect problems or at minimum keep the numbers under control so other predatory insects can come in and finish up the rest.
Hope this helps. Both of the products I mentioned should be available at your big box stores and "most" garden stores. As always follow the instructions printed on the labels for application strengths and replication intervals.
Edit: Fukien teas are known to be pest magnets so your experience here with these insects are no wrong doing on your part, bugs just love the taste of this plant.
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