That would be HORRIBLE news.  If that's true, I'd IMMEDIATELY stop using Shakepay, and would withdraw ALL my funds of all types (crypto and Fiat).

If they are not pooling the funds, and sending out different coins than they are receiving, then it is impossible for them to maintain any reasonable amount of cold storage! This is a HUGE security risk.  It means that ALL private keys for ALL crypto funds are accessible electronically.  It means that FAR too many employees in that company have access to EVEERYONE's private keys.  That would be a disaster just waiting to happen.

My hope is that what really happened is the following:

Previously Surmount interacted with this ForEx broker and asked them to send some bitcoins to an address at Shakepay.  The broker entered the requested address into their system as being an "account number" for Surmount.  When Surmount now, later, requested a new transaction, it was a different address than the first time, and therefore the ForEx broker refused out of concern that sending to multiple "accounts" could be a sign of money laundering.

If that is what happened, then it's still possible that the funds that the ForEx received were still from some pooled funds, and that the ForEx broker is not looking at the transaction from Shakepay and trying to discern an address that the bitcoins "came from".

In this case, the ForEx broker needs some serious education about Bitcoin.  Addresses are NOT "accounts", and in bitcoin there is no such thing as a "sending address" or an address that the bitcoins in a transaction "came from".  A single "account" at custodial service can have an uncountable number of addresses. I would not trust this ForEx broker with Bitcoins until they can demonstrate that they understand some basic facts about how Bitcoin transactions work.