Certification Academy review: Overdue Invoice since June of 2024

I have been trying to collect on an overdue invoice since June of 2024. They did pay $500 out of the total of $4000. At first, they just kept telling me it was "processing" but that never came to fruition. I have been very patient but I'm a small business so not receiving this payment has hurt my company. Now, they are threatening me with a lawsuit just for asking for my money! They claim I'm harassing. How am I harassing when I'm just asking for what is due. I hope no one else gets treated like this. Also, I don't understand this website. No one has EVER responded to any of my complaints. Wish Certification Academy would just do the honorable thing and pay me what I'm owed. That would do wonders for their reputation but I'm not holding my breath. It's just very disheartening when a company doesn't pay for a job successfully completed. It's a shame...