If the calls continue, speak to your phone service provider about whether they can provide documentation evidencing the dates, times and number initiating the calls. The phone company may require a subpoena. Provide this documentation or some other form of proof that the calls are occuring( photos of a caller ID) to opposing counsel in another straightforward but firm letter to opposing counsel demanding they stop the calls. If the calls continue you might want to consider supplementing your claims to include these actions.
A simple solution is to block that number. Call your phone company for guidance on how to do that.
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