I thought the endorsement had to be lifted before the dam's owner could breed from her too.
This might be why the breeder & dam's breeder have fallen out.
I hate to say this but the endorsements are placed for good reasons & if your breeder has just gone ahead & had a litter without contacting the dam's breeder then i guess they would be quite upset about it.
I hope for your sake they can resolve this.
Personally i would contact the breeder again & again until i got answers.