10.5gb used on Portable Wifi Hotspot App in 10 days?!!

I received a txt from my provider today saying I have used up 80% of my data allowance... My bill period is from 26th to 25th of each month & I usually only use 4-5gb of my 15gb allowance over the whole month let alone almost 13gb in 10 days!!
When I checked my Fone it says that over 10.5gb has been used up by 'portable Wi-Fi hotspot app' of which it all went on 'background'...
I haven't had the Hotspot on at all for ages and definitely not since my last billing date...
I can't find this app anywhere on my Fone... In my app drawer or app settings... Nor can I find any info. on it on google!!
In the Hotspot setting it's showing as 'turned off' & no-one is connected... I have the usual security settings on it...
Can anyone help please?
I have Wi-Fi at home which I use when at home most of the time & I've only used around 1.5gb on other apps other than this... It's very worrying!
I have a LG G4 running Marshmallow