Police in Natick, Woburn and Wilmington were sent on hoax emergency calls last night — the latest string of false reports after dozens of bogus bomb threats were called in to schools earlier this week.Woburn police responded to a 6:53 p.m. call from a man who said he had harmed his mother in an apartment on Westgate Drive and threatened to harm others.The caller remained on the line with police for some time, said spokesman John Guilfoil, as police and regional SWAT teams descended on the cluster of apartment buildings near Interstate 95.