Many thanks for your patience, it is appreciated. I am now pleased to be able to provide further assistance with your query. First of all, I am sorry to hear about the issues brought up by this. It must be a frustrating situation to be going through.
The main thing to consider is whether you had formally accepted their offer, rather than just it being a tentative acceptance, with an official, one still to come. That would depend on what was said and if it was clear on your part that you had accepted the offer and were proceeding with it. If that was the case, a contract would have been formed.
Sometimes, an employer may change their mind with a recruitment they have made and decide to withdraw that offer of employment.
If the offer was conditional on anything such as references, background checks, etc it can be withdrawn if any of these conditions have not been met.
However, many job offers are unconditional, which means that a legally binding contract would have been formed as soon as it was accepted. This places certain obligations on both parties – the worker would be expected to commit to the job and start it as agreed and the employer would be expected to employ the worker as promised.