that was devious to make it appear you received jewelry. failure to abide by a trust agreement is considered estafa. unfortunately, you agreed, and now the burden of proof is on you to disprove what is stated on the agreement because it is presumed to be true.
does the demand letter refer to the jewelry?
what you will need to prepare now is your proof that this was just a loan. gather your witnesses who can help you.
to rescind a loan contract, the proper recourse is to file a complaint in the RTC. i would recommend this step because they are poised to file a criminal case against you.
incidentally, 10 percent interest, if per month, is unconscionable and should be reduced accordingly. good luck.