Unknown phone

I took my Samsung J1 for repairs at vodacom walk in centre in midrand, i was assisted by 2 guys and they told me they needed to load an operating system on the phone and that i should return the next day to collect my phone. They did not give me a receipt or a reference, and i walked away. Unfortunately i was unable to go back to vodacom the next day, but could only go the following week. When i got there, no one knew what i was on about and until today my phone is missing from vodacom's premises. The phone was bought in cash and it was fairly new at the time. The phone serial number is ***. Can someone trace the whereabouts of this phone and advice. Thank you