voltage on the battery; it was 0V
This looks like a dead battery.
Li-ion battery can get damaged if it was over discharged or staying at zero charge volume for a period of time. It could be that the seller forget to completely switch off the machine after testing it before the dispatch, letting it on standby or sleeping mode which will still slowly drain the battery. Plus you mention it got caught by custom for months, the battery could have been damaged with zero charge for months.
You should claim a DOA from your seller.