WIFI ROUTER USES DATA WITHOUT ANY VISIBLE CONNECTION... GHOSTS MABY??

For me GOOD & BAD i have monthly data & wifi, i discovered that my wifi data is being used even though im 15km away from home, with prove no else is linked onto my wifi, no other devices is backing up etc. HOW DOES IT WORK does the wifi router use my data without my concent? i have send several emails and still cant be explained to why, after sending my screenshots of no extra devices i was told it is because im connected YES im connected because im at home not 15km away...