I bought an Infinum light, didn't get it to work. Same symptoms as you guys, SIM cards were working separately but not with adapter. I payed about 56,- EUR for a thing that doesn't work it's nearly half of the price of my Xperia mini ST15i, which is quite a lot, maybe not for people in Switzerland, but for me yes. I opened a dispute via Paypal, they declined refund and pointed me to their tech support, which forwarded me messages with instructions and video. I followed all the steps before opening dispute without any success.
Did anybody opened a case via Paypal? How it eneded?