Can my attorney file a motion to withdraw due to non-payment when they failed to bill?

My attorney sent me an invoice 14 months after I paid my initial retainer. It was a divorce case and we were not in court for a six month period but somehow there are charges for "work completed on my case". I had no idea that my retainer had run out nor was I aware that I was accruing a balance. I received the first invoice two months ago and now my attorney wants to withdraw from my case for lack of payment. After I received the invoice, I was told by the receptionist that a payment plan was no problem and she would talk to the owner and get back to me. When I didn't hear from her, I called back where she then stated that a payment plan was out of the question and they were putting in a motion to withdraw. I told her I had no problem paying the bill. I just needed some assistance since they took over a year to send me an invoice. I have paid them an additional $1000 on the $5000 balance and plan on having it paid off soon. I was one court date away from having my divorce finalized. Can attorneys just abandon their clients due to their poor billing practice?