This program has also the ability to convert files to other formats. This might be the reason why your output file is much larger than the original one. Also, it seems that the program is fully compatible with the new operating systems, like Windows 7 or Windows 8, so the problem with your Windows Mwdia Player could have another cause.
If you want to obtain a refund for this product, you need to contact the developer directly. There is no other way to do this. However, there is noting mentioned on the official website about this matter. To contact the developer, use the Support section from the mentioned site.