cannot hear people on pther linevery loud on the other line, sounds very low or weak

I just bought a phone online and need to know if its a quick fix or do i need to return, its a s8 plus, anyways when i make a call i can barely hear what they say. Any ideas to fix it, or send it back? All answers are GREATLY APPRECIATED. I can hear people on phone calls, just sounds very weak and not great its just real low. It doesn't matter if i turn up call volume or not. It's kust the earpiece, other speakers work excellent

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