Very Unprofessional not Trustworthy

My geyser was replaced by this company 0n 14 December 2022 with a firm commitment to issue a Certificate of Compliance and Invoice. The aforementioned required to complete my insurance claim and recover the funds from my insurers. I paid on completion of the work, more than a month later after numerous calls and messages I am just told that they are "busy with it" open ended responses despite promising to deliver the COC on completion. Not trustworthy, reliable or professional.