Harrasment

I am a client of Cartrack and currently behind with my payments.This company is now harrasing me. I wonder what the law says about this but I will find out.They phone me everyday and bombard me their call and SMS.Monday to Monday any time.The last time I check, a company you owe can phone between 8am to 8 PM BUT TOTALLY NOT ON A SUNDAY. Its now 20:58 and have receivd an SMS from them.They do this even on a Sunday before 8 am and throughout the day.I have this on my call records.