Be paid or don't work.

I am so deadly serious - do not continue working if your invoices are late.

You don't have to be a jerk about it, just explain to your primary contact that you need to be paid and you pick up tools again when the money has arrived.

BUT it is on YOU to properly negotiate reasonable payment terms. And if you don;t know or don't trust the client then require payment in advance until a stronger commercial relationship can be settled in. Do not be a baby - go research business contracts and payment terms.

Do not be afraid to lose business from companies that are squeamish about paying you - in fact actively avoid such companies.