I had started a project with a fairly new client about six months ago. Up until three months ago, they had been paying me without delay, but unfortunately, my latest invoice is currently unpaid and reaching the three-month mark of non-payment.
My usual payment terms are either immediate payment or a maximum term of 30 days. I've told the client explicitly that I cannot wait around for them to pay. They've responded that they will pay, but they haven't. This has been ongoing for three months; I've kept emailing them, but they have not paid.
I currently hold physical assets from the client; I have told them that if they do not promptly pay, I will have no option but to discard or sell these items to help make up for the outstanding invoices. However, they've said that if I take these actions, they will bill me for the total amount of the assets. They've also said that I would need to forward all completed work as per the NDA and the company's Terms and Conditions.
As a freelance contractor, I do not want to work for a client who cannot pay on time, so I want to cancel the contract. Would I have full rights to cancel the contract and void a signed NDA? What options do I have with a non-paying client such as this one?