(Not a lawyer, but…) Definitely stop working. Do announce to them why you are stopping, so nobody can claim you abandoned the project. While a call is useful,

(Not a lawyer, but…) Definitely stop working. Do announce to them why you are stopping, so nobody can claim you abandoned the project. While a call is useful, always follow it up with an email summarizing the call (date/time of the call, summary of what was discussed or what you mentioned to them). Useful for the timeline, and in small claims court, or handing the debt to collection services. If there are any remaining deliverables, provide proof of the deliverable being ready via email, but provide it in an unusable format (e.g. with copyright message, watermark, smaller size) and state that it will not be released until payment is received. It sets up a timeline. Don't fall for the "just send us X and we will pay you". Tip for the future: If a client exhibits a tendency to pay late, I place key assets (javascript, CSS, images) on my own server and link to them from their site. Once the work is paid for and/or the project completed, I upload stuff to their server on the hand-off. If they don't pay, I have some leverage, e.g. archiving these key assets on my server ("to make room for new projects") will impact their site. Depending on the assets you chose to self-host, it won't be easy to hand off your work to another developer either until they've paid for it. PS If you need the client as a reference or is a big name that might lead to more business, staying on good terms is sometimes the better decision. Still stop working!