// actually you cannot load the pack onto an ox if the ox is not standing near the pack anymore. This was something that was exploited at one time. It's not possible to actually steal an ox pack, but it is possible for a GM to destroy one, which may be done if it is left unattended.
It is important that one manages one's ox pack carefully. Always, always, always load the pack back onto the ox after loading or unloading. To do otherwise risks loss of the pack and its contents.
As for what you can do...if you cannot access the ox pack from the conversation, you will probably need a new ox. Unfortunately, you cannot get a new ox until the old one dies.