Bizarre problem with 3 phase WYE system
After 4 interventions by the utility over a 2 month period, each time they they showed up the technician (a different one each time) denied that there could be a problem at the pole, even though I showed them an experiment that proved it was on the utility side. They changed the main breaker, which did have a burned contact but this wasn't the cause of the problem and the other times they made invalid excuses and left.
Eventually a friend contacted someone he knew higher up the ranks, and he showed up with an experienced technician. The tech climbed up the pole and remarked immediately that the neutral wire was burned, repaired it and problem solved in less than 30 minutes. The Third World works like this unfortunately. But I'm happy my electricity is back to normal.