I would advise first calling your state department of education (special education department) and asking what they think. You don't want to start a fight or pay for legal expenses if you don't have back up from the state. States have been very lenient toward school districts during this special education teacher shortage.
One thing I would ask for personally is if the offer could be used DURING the school day. School districts contract with outside providers all the time and provide services during the school day - sometimes via Zoom. See if you could work something out.
We do not provide legal advise on this site, but a couple of things jumped out at me. First, they are referring to it as an "offer." Does this mean if the parent can't arrange for services to be provided outside of school that the school district is off the hook because the parent "rejected" the offer? That doesn't sound right. (Not to mention that transportation should probably be "offered," as well.) Second, you make a good point about other parents who don't have the resources or aren't savvy enough to understand this "offer." Is the school district going to follow up with all parents to confirm that minutes were actually provided? After all, the school district is the entity that owes the child the minutes and has to show proof that they were provided. (Another question to ask the state.)
As far as the school district's failure to respond to your communication, first, I would not call. That leaves no trail of your attempts. Second, when you do not receive a timely response from the person you emailed, go up the chain of command - principal, special education director, superintendent, school board. You might also consider attending a school board meeting and asking your questions - preferable getting other parents similarly situated to attend.