It is very clear that they are not serious, you already know who are responsible for this company, besides they are based in Czech Republic,

Founded: 2013
Headquarters: Prague, Czech Republic
Products: Smart Payin API and exchange widgets
Website: changelly.com

then you should report them to the competent authorities.

You have already contacted them several times and the answer has always been the same at no time do they show that they want to solve your problem. Do not beg anymore, do not humiliate yourself anymore... denounce them to the police and let them answer in court. Use all legal means for them to return what you think is yours.