How to MM K3 Note?

So here is the thing: bought myself second hand 4 month old K3 Note. This device is really awesome and i really, really love it!
Previous owner stated that he ordered it online (GearBest or some other shop, i don't recall exact name).
And here is where it gets tricky with me trying to upgrade it to MM:

- in system settings it says it's Lenovo K50a40
- sticker under battery says it's Lenovo K50-t5

- IMEI numbers in system info do not match those on sticker on the back of phone
- serial number is SN:00000000
- ROM version is K50a40_S205_151118_ROW (5.0 Android)
- TWRP version 2.8.7.0 is working
- phone is not rooted...
- after OTA downloads its patch, phone reboots into TWRP, but i get error message saying: This package is for "Lenovo K50a40" devices: this is a "Lenovo K50-T5".

Now, i have read here on XDA various and confusing forum posts regarding flashing/OTA upgrades/lost IMEI and stuff, and i am really not sure about the way how upgrade is done properly.
Since i can't imagine i am the single living person with this kind of problem, i am looking for kind soul to help me out. :good:
Many thanks in advance!

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