What are my rights if I tried to pay as much as I could?

Hi, I have a 11yr old son who moved to Canada with her husband & 2 other kids to him in Jan 2012 ive not see him since then although my x & i had an arrangement to carry on paying his money into a account I set up & use that money to go & see him.

I was made redundant in Nov before they went & struggled to find a job but Feb 2013 i manage to work with an agency who kept laying myself & others off every couple of months. Altho i couldn’t afford to keep up my monthy payments for my son altho i admit this is not enough but i did manage to scrape money together for his birthday Xmas and also whilst one day speaking my son he asked can he have a I PAD to do his school work on which i managed to.

So i was working for agencies on & off for approx 15 months but in Aug 2013 i manage to get a job non agency job which is my current job and ive started payiny money for my son again but into my ex’s uk account shes threatinig to get CSA involed to recover the months i missed.

Please can you advise me on my rights as to were i stand on this matter?