The initial error:
undefined method `initial_date' for #<Class:0x7f30aa1ea398>
Is probably due to the fact that you're calling initial_date
on insurances
(which is an array)
What you'd want to do is pick the specific insurance you want to work with. So it would be something like this:
policy.insurances.first.initial_date
or
policy.insurances.last.initial_date