Helicopter pilot reported a NMAC with an air carrier while receiving flight following from ATC.

Narrative

Departed ZZZ. Contacted Bakersfield Approach for flight following to RNM in [a] helicopter at 9;500 ft. and was assigned transponder code with current PA (Precision Approach). Quality communications maintained. Contacted Joshua Approach when directed. Confirmed hand-over and updated advised PA. Maintained 9;500 ft. and constant radio communications. Contacted SoCal Approach when directed by Joshua. Confirmed communications with SoCal; updated to correct PA for the area and was advised to maintain altitude 9;500 ft. and cross ONT mid-field before continuing own navigation to Ramona. Changed heading to intersect ONT mid-field maintaining 9;500 ft. and constant radio communications. Once clear of the below Class C ONT airspace (2;700 ft. to 5;000 ft.); still maintaining 9;500 ft.; I contacted SoCal approach on 134.00 as directed. Confirmed good communications with SoCal approach who requested that if able to I can descend to 7;500 ft. I confirmed read-back; confirmed that I was able; and that I would commence a steady rate of descent to 7;500 ft. as instructed; while maintaining constant communications. Having leveled off and maintaining 7;500 ft. as directed; I (and other aircraft.) continued to receive traffic advisories for aircraft. in the area; including an advisory relating to possible wake turbulence; but no vectoring instructions were given or received relating to the aircraft. I was piloting. Constant quality radio communications were kept the entire time. In the proximity of Temescal Valley; an audio advisory relating to an aircraft. approaching at my 7 o'clock (behind and out of sight) was received; immediately by an air carrier passing directly beneath me at an estimated less than 5;600 ft. and traveling in the same direction. Pilots aboard the air carrier; that were monitoring the same ATC frequency as myself acknowledged and advised of their receipt of an RA relating to the helicopter. At the time of the incident; I was maintaining a constant heading; altitude; and communications exactly as I had been instructed by ATC. And by all account the other pilots of the air carrier were doing the same; maintaining a constant heading and following ATC instructions. Sometime after the incident I was contacted by ATC and advised to call them on completion of the flight at a given phone number for pilot diversion. Navigation was continued unobstructed later followed by frequency change instructions to descend to 5;500 ft. and advise of receipt of info XX for Ramona; which I complied with and notified accordingly. When advised by ATC I contacted Ramona Tower; advised them of my intentions and was given appropriate clearances. Ramona ATC did advise myself and the other aircraft. within the area that they didn't have the ability to supply flight separation services at that time. Adamant that I was innocent of any wrongdoing; I contacted SoCal ATC on the number given. A recording of the call was taken. The call was very brief. The call taker; having reviewed the tape of the incident; did not think there was anything to report and was uninterested in talking to me.