Protection from Power Utility issues in 3rd-world country

The power utility miswired the transformer, connecting one phase to ground. This rendered 220V between phases, as normal, but 384V between hot and ground on at least one or two of the three phrases. My home uses all three phases, connected through a single 3-phase meter. (Most homes here do not use grounded outlets, and I have added ground on my own.)

I complained to the power utility, who at first tried to deny the issue. When confronted with the evidence, they admitted the problem and said they would fix it. They never came back. However, more than six months later, I tried to find the 380V readings again, and could not. Everything was 220V. So, thinking it was fixed, I hooked up my desktop computer to a grounded outlet via a line-interactive UPS, and ran it perfectly…for a week. During a lightning storm last week, suddenly the 380V came back! My UPS was fried. I haven't tried the computer yet, as I don't trust the power. By afternoon of the following day, though, it had returned to 220V, hot to ground, just as before the storm.

What might the problem be, and what can I possibly do to make the electricity safe for my computer?