Nokia — Change my phone battery

I am Souvik Santra, Belong from Tarakeswar, Hooghly, west bengal. Few days ago I submitted my Nokia 6.1 plus mobile phone in our nearest Nokia authorised service centre die to charging issue. The service centre take my phone arround 12 days. However when I received my phone, I see that my phone back panel is not set properly. So I asked them but they told me that the gum problem. But when I using my phone I noticed that my phone battery charge % is drop down very fast. So then I visited another Nokia authorised service centre. They said me that the battery is duplicate. We are not expect this type of thief from Nokia authorised service centre. Hope I get help from Nokia as soon as possible.

Regards
Souvik Santra