My iphone alarm/clock appears to have been hacked

A week ago my Alarm went off at 3.30am, I pressed snooze, alarm went off again, I turned phone off completely, In the morning I checked my iphone clock alarm screen & noticed just under the 3.30am marker a short message had been inserted on the screen, as follows "Alarm clock is a bit difficult etc,

altogether a 21 word message some in broken English,

it appears that the iphone clock cant be completely deleted, I understand this is normal, I have just left clock on international time & use a separate alarm,

for the record, my phone is in my permanent possession, my phone is never lent out, only essential apple store apps have been loaded,

any advice greatly appreciated