Is it legal for my ex-husband to file child custody papers without serving me papers?

Here about almost a month ago, I was supposed to meet my ex husband so I could get my daughter for my week. We had joint custody, week on/week off, neither of us had to pay child support. We were supposed to meet at 6 PM, but when the time rolled around, he didn't show up. I tried calling his phone, but it was out of order, so I called and texted his new wife several times, but still got no answer. I sat there until 6:45 and notified my ex husband and his wife I was headed home and to get a hold of me when I needed to get my daughter. Saturday came, I called and texted, still no answer. Sunday morning, I wake up to a text from him Saying I no longer had joint custody and that I now had supervised visitation and that I was 5 months behind on child support. I literally thought they had the wrong number and asked what they were talking about and they didn't tell me. I looked myself up on online public records and come to find out he filed back in March and said that I failed to appear. I was never served papers. Just would like to know how this could've happened without my awareness and right to fight in court. On top of it all, he had still been giving her to me every other week for my week even though he said I needed supervised visitation every other weekend. I had still been getting her for my week up until a month ago, 3-5 months after the court ruling.