Instead of Change of Flight Charge, 2 x flights!

I booked a flight back from CPT to PLZ for 1 June 2015. I received news that I would be required to spend two extra days in CPT, so I EMAILED as below:<br> <br> Hi<br> <br> I have tried several times to contact Mango to change my flight from cpt to pe tomorrow (Monday) morning at 07:30.<br> <br> I need to stay two extra days, so would like to change my booking to Wednesday morning.<br> <br> Please respond as soon as possible with confirmation and how the extra charge works.<br> <br> Many thanks<br> D***x ******<br> 074***<br> <br> I received an invoice which I saw tthe new flight, which I assumed to be the fee for the amendment.<br> When I inspected it for travel claim at work, I discovered they had simply charged me for the extra flight ON TOP of the original Monday one, including all extras. <br> <br> I would like a full refund for the Monday flight asap.<br> <br> Regards.<br> D.