澳大利亚采购需求：超声波诊断系统、多普勒超声波、黑白超声波、兽医超声波、二维三维超声波、

I need to lodge a formal complaint regarding a veterinary ultrasound machine I purchased months ago. Unfortunately, its image quality didn't meet my needs, and I was told by your sales rep that I could return it for a refund. I've returned the machine but have yet to receive any refund despite numerous follow-ups. The lack of communication from the sales rep has been extremely frustrating, and I would like to speak with a different representative to resolve this matter. It feels unprofessional to be left in the dark like this after returning the product. I expect a prompt refund as previously promised.