They have only email and simplex contact I tryed already both…
That is good. You will have letter of guarantee after you have done t the money to the address they provided you. To make it faster, include the letter of guarantee in the email. If you do not include it, they will still ask for it.
How long has it been since you contacted their support? I would say give them up to 48 hours to respond. Don't forget that July/August is holiday season. People are on vacation and therefore you can expect delays with whatever you do. It's normal. I understand how you might feel, but eXch has thus far had a spotless reputation.
I think h has just sent them email and the other way to contact them. I hope they can solve the problem as fast as possible.