@OP I think your withdrawal tx got dropped from bitcoin mempool due to low fee payza might have included in that transaction. If it is true than those bitcoin should have been returned to them, you should contact their support and wait for their answer. They should process your withdrawal again with higher fee.
I have just contacted their support for the second time. Let’s see.
To sum up so far: Firstly, I received that email from Payza saying that my transaction was completed; then, after many days seeing that my transaction was still unconfirmed, I contacted the support for the first time, but didn’t get a solution. My hope was that the bitcoin, after weeks unconfirmed, would eventually 'drop' into my wallet. It didn’t happen, Payza didn't return the money to my account, and I am at a loss now.