Not sure how seller did this but I offered $400 and they charged me 1,350. How do I stop this

Offered $400 but was charged$1,350. Seller is not returning. How do I get ebay to step in | Ask a Mentor

Offered $400 but was charged$1,350. Seller is not returning. How do I get ebay to step in | Ask a Mentor | eBay Community