[mothered]

If I have any possible allergies which I decline.

You should've said you're COVID-19 positive.

Call them back, and say you've just received your test results and have the virus.

But why would they want it back when it's of no use for them at this point that I had allegedly used the product. It's a 1kg container.

They may take It up with the manufacturer to see If It's a defect causing Illness.