Just terminate .... You really don't have to give a whole if reasons .... You could just say ...
Dear xxxxx
This letter is to serve notice that due to ongoing behavioural issues and a general air of disrespect to myself and my business that I will no longer be providing care to xxxxx. The last day if available care is ..... All fees are still required whether xxxx is in attendance or not.
Regards .....xxxxx


Make sure you get your payment Before handing out the letter. Keep a copy for yourself.