Use of data without me being on the APN

I went abroad on 9 January 2018, upon my return, I found that my data was being used, even though my sim card was with me in Germany, in my wallet. a week later I received an SMS and email saying my data is almost depleted, all this while being on my MTN APN after my return.

Seems they are doing what MTN was doing to their clients and using data for absolutely nothing, even with an APN not being switched on.

Call center and support staff has also been terrible, not willing to assist, not replying to my emails and even just refusing to assist in transferring me to someone that will be able to assist