If you are absolutely unable to contact any TOCs, NRE or NR, and you are sure you cannot use the help points or platform/level crossing phones, I would suggest you call the BTP - you may wish to call 101 (the non-emergency general police number) and ask to be put through, if the BTP number is not displayed or you can't remember it. It is totally unacceptable to leave a passenger stuck on a platform all night, especially if you are in a remote location on a cold evening (for example).
In the highly unlikely event that you are unable to carry out any of these actions, attempt to flag down any engineering train or ECS move, if there is one. I am sure that, if it gets this far, a train driver will be happy to put a call through to NR.
Under no circumstances should any passenger trespass on the line in order to access a telephone! Due to the natures of unpredictable train movements, electrification (including any exposed signal cabling), trip hazards, and also structures/phones with Limited Clearance, it is safer to be stranded!