Recently bought an '08 Astra Breeze 1.4L

Check engine light came on after a week. Mechanic checked code and it was Lambda sensor. Reset and check engine light reappeard after couple of days.

Replaced sensor now when it's down to quarter of a tank engine starts cutting out and losing revs until I put petrol in again. Repeats every time fuel gets low. No fuel light pr check engine light comes on and low fuel range info doesn't come on on digital display

Any ideas on cause and how to fix?