Phone receiving "fake" calls,unanswerable as screen remains black.

Wiko phone,these calls started 2 months ago.I removed that ringtone completely,it's still coming through with it,at least I know it's the fake call.Phone remains "off" ie doesn't light up or vibrate,just plays the ringtone.Its happening up to 20 times a day,driving me crazy.
No malware as far as I know,regularly scanned.

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