A bill collector is a person who goes and finds people who haven't paid their bills – money they owe to a company – and gets them to pay them.

收账员是一个去寻找没有支付账单的人——他们欠公司的钱——并让他们支付的人。

He's saying that it's so difficult to find these buildings that no one would be able to find them, even people who are looking for you, such as bill collectors.

他是说要找到这些建筑物太难了，没有人能找到它们，即使是找你的人，比如收账员。