Very important matter to ask here... What should I do next?

1/7/2015
Made a purchase for an electronic item from Lazada worth RM2989
Purchase was made after 5 attempts
Item was SOLD AND FULFILLED by Lazada, so I am more convinced to make the purchase

3/7/2015
Lazada cancelled my order - reason? System error!!!
Process for refund initiated

4/7/2015
Received email saying that refund was logged and processed
Will take 5 - 15 working days to process

14/7/2015
Checked my account, still no refund
Contacted Lazada - told that refund process has been logged and processed, receipt of refund attached with email
Also told need 5 - 15 working days for refund to be credited back

I was being patient, so I waited...

29/7/2015 - ALREADY 18 WORKING DAYS
Still no refund credited back into my account
Called their customer service and made a complaint
Told they will get back to me

30/7/2015
Received email saying refund completed on the 4/7/2015
I told them, if refund process is completed, why still no money credited back to me?
They informed me that the 5 - 15 working days is my bank processing period, not Lazada - WTF??
I contacted my bank and staff confirmed that no pending / floating amount logged into my account since 4/7/2015

Re-contacted Lazada again and made a fuss again
Kept telling me the same thing - refund processed on 4/7/2015 - there's nothing they can do
Sent me receipt of refund again
I lost my temper and scolded the staff

I mean, why you keep showing me the receipt of refund? No point at all...
My bank confirmed they did not receive any request from Lazada at all initiating the refund, so I argued that Lazada should be responsible for this error...
I said if this issue still not solved, I would have to resort to make a complaint to the Tribunal for Consumer Claims...
The staff then requested my credit card number to re-check with finance dept --- which I think they should have did when I initially made the complaint if they really confirmed the refund process has been completed...

So now waiting to see how they will respond... Will check back with Lazada again tomorrow... Anyone experience the same thing as me before to request refund from Lazada? What should I do next? Can I ask my bank to liaise with Lazada for my refund?