This may be a silly question, however do you have the correct Givi mounting kit?
I know from experience that the MKI tracer (2015-2017 that I have) has different mount points to the later bikes for panniers and as yours is a MKIII, this could be the issue.
Sorry I can't help in this particular case, although I can confirm that Givi support is poop. I bought a rear hugger for my MKI tracer last October and it won't fit. I am still hastlng Givi for an answer (3 months later) as to why so I can understand you have issues getting it resolved...