Sometimes when English is not your first language, it is useful to write the problem in your mother tongue and use Google Translate to change it to English.
Then paste BOTH here as a question.
I think what you are saying is:
You bought some plants.
They were Not As Described.
You returned the plants for a refund.
The seller did not refund but offered a partial refund of $20 .
Did you open a Dispute (Resolution Centre, bottom of this page.)?
When you returned the plants did you use a Confirmed Delivery service like Regular Parcel (Canada only) or Tracked Parcel USA?
Do you have proof of DELIVERY (not shipping, delivery)?