Once you reach the max that's it. Having said that, there usually are age-related add'l discounts, ie over 50's etc, a lot of discounts then disappear again after 70. BTW advertising percentage discounts is a marketing swizz, over 70% or whatever is irrelevant unless you know what its 70% of.
I think, you only get 5yrs when you transfer to another company, some companies give you a bit extra for longer. It probably varies from company to company. Also some times you can't have multiple discounts so you might get one for a spouse on the same policy but not for having your house insurance with the same company.
+1 on its a scam otherwise they'd publish the criteria to reduce your premium. As they don't they can tell you anything.