"Chlorine lock" is an old pool industry term for "anything we can't easily explain after selling this fellow all of our other magic potions for problems that did not exist". The next thing they're going to tell you is your water is "old and has gone bad."
What they are referring to, and from what you have described, is that your pool water is over-stabilized. That is, the CYA (cyanuric acid or "stabilizer") is too high. All of that shock you dumped in the pool and all the cranking up of the chlorinator has added lots of CYA to your water. The chlorinator is full of 3" trichlor pucks, they contain CYA. The shock you used was likely dichlor, which also has CYA. So you've basically loaded up your water with CYA while trying to get the FC to register. The problem is that CYA in small amounts (less than 80ppm depending on pool type) is a blessing; CYA over 100ppm is a curse. If you read through enough posts here on TFP and through Pool School, you can learn the science and chemistry of CYA and it's relationship to FC.
So the fix is this - you need to stop relying on pool companies and "pool experts" and take control of managing your own pool water. That starts with reading through Pool School and learning the
ABC's of Water Chemistry. Next, you need to order your own test kits and learn to test your water yourself. The comparison of Test Kits is found
HERE. You must then commit to
The TFPC Method of pool care. And then you'll be totally free of the bad advice that is handed out at the pool stores which is designed solely to part you from your money.
At the end of the day, your CYA level is probably off the charts high and so the only solution will be to drain some of your pool water and replace it with fresh fill water. How much that is and what you'll need to do can only be determined after we get reliable test results of your pool water. You can post Pool Store test results, but no one here will believe them. We typically only put stock in water testing that pool owners do themselves.