S8 duos (exynos) and cell reception problem; faulty hardware or something else?

[hiryuna]

Hi guys,
I have problems with my S8 duos and i want your ingenious insight. I'l try to explain the problem but please keep in mind that English is not my native language.
I've bought this mobile from a retailer on ebay on June17. I'm from Greece and the local samsung dealership doesn't import the duos variation (the supported frequency bands are the same). It worked perfectly for 4 months. Two months ago the cell signal started dropping (I have strong signal in my region) in one sim card or both of them. Sometimes the device worked ok for a day or two but eventually the problem continued to appear (signal going up and down, sometimes stuck to no signal indication forever). Last week the mobile updated firmware to ver g950fxxu1aqk7/g950foxm1aqk7/g950fxxu1aqk7. This update totally wrecked my cell signal. Now the signal is dropped (until no signal indication appears) within a minute of rebooting the device. Only within this minute I can make calls or exchange mobile data!
So far I have tried various things
a) installing sim cards on different cell phone -> worked faultless on 2nd mobile
b) installing different sim card on S8 -> same problem
c) rebooting -> temporary fix 2 months ago (for a a day or two max), now nothing
d) wipe cache -> same as above
e) factory reset -> same as above
The last straw for me was when i started the initialization setup after a factory reset and the problem appeared before installing anything!
So far I've concluded that it's either a hardware fault or something firmware related. I want your help to rule out the firmware aspect.
I've called samsung service and from the IMEI number they told me the selling market for my mobile was UAE (no warranty for me!). From the service provider software tab in the device I read eur/eur/pak. I installed the samsung info app and it appears that the active csc code is eur (correct -> Greece) and csc country is segr/gr.

Do you have any suggestions from me? Is there anybody facing similar problems?

Thank you for the time you spend reading about my problem,
Hiryuna

 

[galaxyfive]

1. Check for contamination or broken contacts in the sim slot.

2. Check your APN settings. Your provider will have the correct ones for you.

Sorry, that's all I have.

 

[hiryuna]

Thank you galaxyfive for your reply,
Unfortunately I can't verify easily the contamination or broken circuits case. From a first look with a magnifying lens I can't find anything alarming but I have to force open the back to be totally sure (i'm not willing to open it in case the ebay retailer replies about the warranty)
I've checked the APN settings in the mobile setting menu and they are in accordance with the provider's for both sim cards.
Thanks again,
Hiryuna