Hi,
Neither "apt-get remove puredata" nor "apt-get purge puredata" did uninstall my Pd 0.47 version. I'm on Debian Stretch 9.5 .
"puredata" is a meta package, that depends on the real components:
$ apt show puredata ... Depends: puredata-core, puredata-gui, puredata-doc, puredata-extra, puredata-utils, puredata-dev ...
So you'd need to unsinstall them also, perhaps "apt autoremove" can do it?
Possibly it is a bug in Debian that "puredata" version X doesn't depend on "puredata-core" version X ?