It is difficult to write this without identifying details. Have also NC'd just in case.
Contact between DS and ExP broke down due to an act of violence towards DS followed by a period of intense harassment and intimidation towards myself. SS and police have been involved, mediation attempted and broken down with no formal agreement in place.
ExP agreed to an undertaking in lieu of a Non-Mol. Many "slight" breaches already (attempting to contact my family, asking his family to contact me, always under the guise of "arranging contact"). I have allowed telephone contact between him and DS so they can maintain a relationship (as suggested by SW).
Unfortunately, ExP seems to be using this as a way to further harass me, which is having a terrible effect on DS. Of course, DS is becoming very distressed during these rants, but is even more frightened of my intervening and ending the call (due to experience of when I have done this previously). I feel I have no option now but to stop contact altogether until ExP makes an application to the court 
Could I (should I?) bring this to the attention of the court, as a breach of ExP's undertaking? If so, is it possible to do so as a litigant in person?
When I made the application for a non-mol, I was able to get partial legal aid. However, my earnings have since increased and I wouldn't be eligible, though am truly unable to afford a solicitor (certainly not a barrister) due to an imminent house move.
Any advice would be very gratefully received.