My question involves a child custody case from the State of: Idaho

What is the name of your state (only U.S. law)? Idaho

I received papers today via mail for a Modification to my current Custody order I have with my ex, Our current order was issued a little over 3 years ago. The first sentence says that my ex has retained this lawyers office in order to obtain a modification of the current on-duty parenting schedule, and they are giving me 7 days to respond, They are requesting that we handle this out of court with a mediator but if I do not wish to do so I have to notify there office and let them know my attorney's information.
All of this comes as a huge shock to me, Our current custody agreement states my ex gets 1 week every 3 months and every other holiday, he has never even attempted to take my daughter the entire time we have had this order. My daughter would not even know who he was if he walked up to her in the store, I have made attempt after attempt to set up arrangements with him but he never follows through or he never gets back to me, he literally lives about 3 blocks down the street from me and had not even attempted to contact me or my daughter since December. And when he contacted me in December it was via text message stating he was gonna mail her a present. He constantly pays me late on child support and owes me over 10,000 in medical bills. I am assuming he is doing this because he just recently got remarried and has 2 other children with his new wife and I am sure he feels guilty or maybe not, But they live in a 2 bedroom house and there 2 kids already share a room so if my daughter was to go stay there where would she sleep? My daughter is 6 just started 1st grade today, and has her own room and bathroom at my house. My question is what should I do and how should I respond? I would feel just horrible if I had to drop my daughter off with him because he is a complete stranger to her.

Thank you!!