You simply have to get across to the sheriff that they are being misled by the claimant...there is no such legislation in the annotated version of section 87 of the CCA1974 with regards to requesting arrears or instalments without the need of service of a default notice and that claimant must prove and evidence that a default notice was issued to enable the creditor/owner to proceed to enforce the agreement.
If a default notice was never issued then they must evidence the termination notice of the agreement.
https://www.legislation.gov.uk/ukpga...-of-agreements