Default Lumia 1020 (RM-875) no calls on LTE

Hello all, hopefully somebody can help me with this, since it's making me crazy.
I have one 920 and recently got a new 1020 from Movistar (Telefonica), RM-875 with 64GB if storage. Everything was great until they launched their LTE network, and when I got a new sim card, I found out the ROM the phone has, comes with 4g-LTE disabled. Off course I did what anyone would do in this situation: I flash my phone with another ROM and I got my LTE working.
After a couple of days I noted that I was only getting SMSs telling me that somebody called me. Then I tried to call myself from another number and it went straight to voicemail. When I changed it to 3G again, calls worked fine. I know LTE doesn't support voice, so the phone should get a "notification" from the network to change to 3g to get the call, but my phone is not reacting to it. I tried the same SIM with the 920 and this one works as expected, when on LTE it changes to 3G to get the call.
I've spent the last two weeks downloading new ROMs to see if any of those can help me, with no luck at all. My last resort is to flash back to the original ROM and bring it back to the shop to see if they can help me. Oh and it's not hardware problem since a friend of mine with the same provider and the same phone, he is facing the same issue.
ANYTHING you can tell me to fix this, will be greatly appreciated, since is like a disappointing to not being able to be on LTE with my 1020.

Thank you!