Best would be if you could add some pictures with their EXIF data, to best understand what the problem might be.
As you have been going already to the service centre and as the lens has been working fine for you up to a certain moment in time - and assuming it has no mechanical or electronic problem - you could do a first test with comparing the results by focussing in Liveview versus focussing through the Viewfinder (indeed the camera uses two different technologies for the two).
For doing this test, put the camera on a sturdy tripod and choose a flat object which will fill at least half of your picture. If it proves that the result in Liveview is fine, while the same picture taken through the Viewfinder is not, one possible solution can be to use « AF fine tune » to correct for a misalignment of this lens with the camera body.
You can find the AF fine tune option in the Setup menu.
However AF fine tuning needs some setup to be done.
Watch the video here https://youtu.be/LcNmRq0fOv
to get an idea of how doing.