question about cancelation of amortization schedule. The client has common and quite frequent situations that some truck insurances get cancelled so it means the amortization schedules in Netsuite must be cancelled also. How to achieve that?

This is the biggest reason I avoid amortization schedules, it's a pain to cancel.

since the vendor bill for insurance gets cancelled (voided) so does the amortizations schedule. Original transactions needs to be removed first, then amortization schedule goes.

So actually its quite easy, you just have just create Vendor credit with remaining amount and then amortization schedule puts with amounts with negative sign and all the future amortizations entries eliminate each other.