You have to differentiate between two types of losses:
1 / Hard loss: you have totally lost the chain of words, because the house has been burned, the dog has eaten it … you are screwed, you have lost everything… so the phrase has 12 words generated from a dictionary of 2048 and the number of possible combinations is 2048^12 = 2^132… accept it and forget, time is such a valuable treasure… take your son and a ball and go play, tomorrow open a new account, and remember that 2 years after the date you registered the name or 105,190 blocks, will be “free” again, set up your alarm.
2 / Soft loss: YOU HAVE THE PHRASE but it does not work in the recovery… there are many hopes that you have success, get to work now:
First step, check if each of your words are written correctly in the following list, if you are not native english (like me) is easy to write them wrong … the human brain is wonderful and sometimes fails (origin of the wonderful creativity).
BIP39 wordlist dicctionay: https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt
If in your phrase there is one or more words that are not in the BIP39 list, then try the one with the closest resemblance to the one in the list, for example:
You have written: ciaw, wich is not in the BIP39 dictionary.
The correct word must be: claw… which is also in the BIP39 dictionary.
If all your words are well written then you will have to build similar word trees for each word, for example:
You have written: claw
But the correct word could be: clap, clay, law… which are also in the BIP39 dictionary.
Start making substitutions and composing phrases to use them in the “Restore an existing keychain” process …
If your mistake has been in a single word this can be relatively fast, if it has been in two, the road will be harder.
Quick tip, nowadays, when you restore an existing keychain, you are able to choose an arbitrary short password, for example “1”, it does not force you to a minimum of 8 and makes the process of “manual brute force attempts” fast.
This is not an exploitable access vulnerability through brute force, the system is very safe and follows the standards, it is a tip to make a few attempts quickly.
This is not a zero-day threat, but soon they will change for sure, this team is working really hard 
Good luck.
