If you can't win with getting a N900 back (you have to keep persisting, they are stubborn people who can't tell the difference between an orange and a lemon), then you should sell that E7 and buy another N900.

I have heard of a few successful cases where people have refused to accept N8/E7 as a replacement device for N900 so my best bet is to keep trying and maybe you can get lucky with getting another N900.

The whole point of running N900 is a load of crap, that microUSB can be easily fixed by a skilled electrician (or you can do it if you happen to have a soldering kits handy). Spare parts for microUSB are abundant so there's no excuse as to be willing to accept N8/E7 as replacement.

FYI: When I refer to orange and lemon, I refer N900 versus the rest of the current nokia devices. The rest are literally rubbish when you admire the uniqueness of the maemo platform that no symbian could compare. However, salespeople are usually dimwitted to know the difference on the platform could mean so much to the end user who are in the know.