Law / Seller won't answer, item hasn't arrived.. Could somebody help me sort out problems for allegro.pl? [6]

I don't speak Polish-sorry but I need your help.
I've ordered a trench coat on allegro and listed the shipping address to England,but the coat still hasn't arrived.
I've tried contacting the seller for 3 weeks,using both English and Polish(using google translate) but the seller hasn't replied to ANY of my e-mails. I see she has logged into allegro almost everyday,but she won't answer. How do I know about the coat's whereabouts,or if she has shipped the coat at all?

It would be great if you guys could help.Thank you.