[mothered]

I've been dealing with them for 1.5 years, dozens of refunds and always expensive stuff, never had any problem though.

Understood.

In such a case, the boxer/refunder should've supported your SE every step of the way. That's what he's paid to do.

Apple investigation service should have called me yesterday (May 4th) but nothing. I'll call them friday if nothing happens.

Yes, do exactly that.

Today is the last day I can return the iPhone, it's a bad idea unfortunately

The duration of the Investigation, may not affect the time frame of your eligibility to return the product.

It's not your fault they're taking a while to complete their findings.