Default Galaxy Note 3MTK6572 Invalid IMEI

Hi, I recently bought a Note 3 based in a MTK6572 processor, but the signal doesn't work, I've tried many methods to solve it but no one has worked, I don't know what to do, can you help me?
Obviously this happens cause the IMEI is invalid.
If you need more information about the device u only have to ask, thank you!