Aix la
Chapelle (one p only) is not an old name for
Aachen as far as I know. It is the French version for French speaking people. The Belgium boarder is only a few miles from the city center of
Aachen. French is one of the two the official languages in Belgium.
Living not more than 45 miles from
Aachen I looked at the telephone book. There are still 17 Offergeld entries. Offergeld is a quite frequent name in Germany, however.