Bought refurbished iPhone six. Battery problems so...

Bought refurbished iPhone six. Battery problems so went to local iPhone service centre.
They ran diagnostics said battery problem. Inspected battery and said that it was a cheap counterfeit part and should never have been sold with the phone as refurbished.
Quick fix mobile have refused to make good quoting three month guarantee on batteries. Except this wasn't a quality assured part was it?

Avoid at all costs.