Need advice - Received cut heroin and dealing with vendor : DarkNetAustralia | Torhoo darknet markets

This was my second order of 14g from a trusted vendor, the first 14 was amazing, when I received the second 14g I could instantly tell it was cut, it was not making me high and caused me to go through withdrawals and no matter how much I took it would not quench it, I took 500mg via IV over several doses and I didn't even nod off!

I contacted the vendor and they told me to ship it back, I was obviously hesitant shipping it back and tried to offer a way which we could trust each other. I was going to put funds in escrow whilst they shipped a new batch, then I'd return the old stuff and then they'd release the escrow funds back to me.
They told me if I didn't want to send it back that they would offer me a 50% refund or if I got the product tested and there were any cuts they would offer me a 100% refund. I ordered in some heroin purity tests and I was shocked that it resulted "very low heroin content", the lowest it could go. It also didn't mix in properly and acted like an oil. When I mix up a shot I can see an oily substance on the surface.

I did all of this, then arch went down so I contacted them on abacus, I sent them the test results and they said they'd look into it. They're still telling me to ship the product back, not honouring their 50% refund policy or 100% refund policy. I'm more than happy to send this bunk gear back to them but I have not received any refund. They said if I didn't want to ship it back I could get a 50% refund, now I should be expecting a 100% refund considering that the heroin came back as "very low heroin content" and is completely unusable.
Should I send it back to them? They are a trusted vendor. What can I do in this situation?
Thanks