Need help or suggestions

I am so frustrated with what has happened lately and wondered if any of you out there have any suggestions to offer.
Sorry, it’s kind of a long story.
In Nov 2015 I met my deductible so decided it was a good time to get a new pump and CGM. I chose T-Slim and Dexcom.
The T-slim Rep ordered all the supplies but at the same time the Dexcom rep also ordered the Dexcom supplies (1 box of sensors, a transmitter and a receiver)
When they arrived at my home, I realized they were duplicates and didn’t need them. I contacted Advanced Diabetes Supply and requested a return label. They sent one and I sent the supplies back through UPS.

Here’s the trouble - I learned in January that UPS lost the package. I made the mistake of giving the package to the UPS guy that comes to my office. He didn’t scan the package so UPS, although have helped as much as they can, have stopped helping.

Friday I got a letter that Advanced Diabetes Supply sent me to collections for $1782!!!

They knew what was going on with UPS, I have kept them up to date during all of this.

I called 2 Dexcom reps to request whatever help they could give me. When I first touched bases in Feb with one of them he seemed willing to help. Told me not to worry about it. then I received the collection letter and I can’t get him to return my calls.

I spoke to Advanced Diabetes and all they would offer is a $300 discount, less than the collections agency offered!!
I’m so frustrated. We all know there is a significant mark up on the supplies, I feel like they could have done something to make this more palatable. But they were unwilling to do anything.

And the Dexcom rep, really? Won’t even return my calls.

So I will be sent to collections for $1782 when the only reason I went down this road is because it was supposed to cost me nothing out of pocket!!

Does anyone have any suggestions for me? I have never been sent to collections. This is really going to mess up my credit. I am beyond frustrated!!
Thank you for any help you can offer