Having been in your position, without this forum, I was forced to do some desperate stuff. It is a lot of work, but I have no other ideas, so I will pass this on to you.
I am assuming the old pipe joint has an expanded "female" end on the part of the pipe you are replacing, with small splits 180 degrees apart, as that is how my cars were made.
I cut the old pipe off with a hacksaw just behind the joint. Then I located the splits, and used a Dremel tool or a hacksaw, and extended the split to the end of the pipe stub. Then I banged a chisel in the split line and separated the outer pipe remnant from the inner pipe.
Once before I just drove the car around until the pipe fell off. That was more dramatic and less physical work, but I do not recommend it unless you have no tools and it is Sunday night.
I hope this helps, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)