Help T.T Sim locked and looking for a new phone for bought sim card...

Hi all!

Quick background story - I bought my Samsung S6 edge from KDDI, Japan. Phone was unlocked in Feb 2017, and then I moved to Italy. Thinking that my phone is already unlocked, I bought a 4G sim card from TIM, but my phone responded with "network locked".... I returned to TIM twice, and called up KDDI in Japan three times. TIM said that my phone is still locked, and as for KDDI, they confirmed that my phone has already been unlocked, but unlocked SIM might not work for some SIMs in some cases...
I was infuriated with the response, of course. I paid to have the SIM unlocked and now it does not work!

Bummer.

In any case, I got over it, and am now looking for a cheap smartphone on amazon that I can put my TIM sim card into to utilize my data plan. Can anyone please recommend a cheap, unlocked smartphone that will be compatible with my bought sim card? If not mistaken, it's a nano SIM, the size that fits into my S6 edge.

Thank youuuuuuuuu!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1