I would strongly suspect that why they are paying in advance is because they get paid a commission on the insurance premium.
What they should be doing is handing the 5 largest debits over to a debt collector to recover the money and any penalty interest accrued. The cost of recovering the debit is borne by owner in debit.
Once these have been collected go for the next 5 making sure all owners are aware of the process especially the extra cost the debtors will incur once its handed over to the debit collector.
You might need a motion passed for this to occur but those in debit cannot vote anyway so shouldn’t be a problem.
Yes you are correct the SM works for the owners and the owners decide whether to raise a special levy or not via voting on a motion.