Expedia Delta Airlines Ping-pong between Expedia and Delta Airlines Internet

I purchased 3 tickets, 7 months before my planned trip. 2 weeks after purchasing said tickets, I received email saying my departure flight has been changed. Following week, my arrival flight has been changed. I contact customer service and they contradict themselves, give false information, and decline any assistance but inform me that I'd be charged FOR THEIR CHANGES. I spent 5hrs today between both companies, being hung up on twice, can't get through three times and being mislead each attempt. i learned that Expedia purchases tickets from Delta, so this issue is an Expedia problem not Delta. Expedia sends me to Delta, Delta sends me back, they both contact each other and hang up on each other.

How can i get any resolution when they can't work together as a business. I'm told I may or may not be issued a voucher if the airline approves, but the airline says it's the travel agency's [Expedia] problem. I contact Expedia and they tell me that Delta would have to approve it once Expedia sends the request cause my money went to them. Do we see the contradictions? if Expedia pays Delta for tix and sells to me, my money went to _________? The answer would be Expedia. Expedia's excuse for that flawed reasoning is that Delta would have to find the basis for refund, this coming from a Supervisor. I explained if a level 1 rep was able to find the difference amount and a basis, why can't the Supervisor? I am fed up with the run around. My vacation is ruined before it begins.