I optioned a script to a foreign company a few years ago, and after the company extended the option a year, days before the final option expired this month (when the rights to the script would revert to me), the company negotiated an additional extension, which I agreed to in a signed amendment. However the final option has since expired and the company has yet to pay me for the new option agreed to in that amendment, and they just informed me that they are unable to make payment until Jan, so they have not technically exercised the new option.
I am not in a position to wait a month to receive payment, and additionally there has been interest in the script from other parties over the past few years, and I am considering exploring that interest in the interim as the rights to the script are mine again until the new option is exercised. My entertainment lawyer who originally negotiated the deal no longer represents me.
Without reviewing the agreement, it would be impossible to offer any suggestions. If your previous attorney is no longer able to assist you, you should find a new one before you make any decisions.
Difficult to say without reviewing all of the documents. Does the amendment require the payment to be effective? If not, then you would probably have a binding agreement and they are in breach of the payment portion of the agreement. In that case, what does the agreement say about terminating the agreement for breach? These are the basic questions I would ask to see what your rights are.
Legalities aside, the 1st few words of your query "a foreign company" will most likely make it difficult for you to enforce whatever documents you've signed, assuming you're required to sue them, if at all, in their own country.
And the likelihood of any other company wanting your script are small, since any chain of title inquiry will tell them that their foreign company has this claim.
To have the documents analyzed for the specific language that the parties have agreed to, you'll need to see your own (new) lawyer. The question also arises about your old lawyer who no longer represents you --is there a malpractice issue there? A discussion you need to have with your new lawyer.