Denise,
Go in to the place that did the original job and just ask to speak with the owner. (When they tell you the owner is not there, etc, then ask for the service manager.) Explain what happened, and that you believe that one of the employees broke the sensor. Advise them you have the blue zip tie that the Ford dealer removed after repair, which was obviously not a factory component. Be nice, but determined/firm. Tell them you understand mistakes happen, but the fact that the tech tried to fix the damage without telling you or informing them (The service manager there) is not good customer service, and is frankly dishonest to their company also. (Who know what else that tech may have not reported) If the manager wants to make it right, then great, if he denies they did anything wrong then ask for when you can speak to the owner, or how they can be reached. If they give you a phone number, call from the shop. Dont give up. Be prepared to go in there every day if needed, and ask them if the owner is available. Just be polite when you go in and ask. You can also call the BBB and file a complaint, call the local news stations for help, etc if they still dont make it right.
Another thought, is they "Asked you to take it to Ford".. That opens the door for you to present them with you findings. Ask your Ford dealer to put on the invoice what was found. (IE: Found TPMS sensor was broken, and had been "zip tied" together which did not hold) They dont have to say who worked on the car, just what was found. You have invoices from them showing what work you had done, so they will know they worked on it previously.
In these matters, the longer you wait to confront them, the less chance they will accept the blame...
My 2 cents...
Dave