seller wont refund me after i returned the item and they keep saying the will refund me? any help?

[iampoochini]

i bought a samsung s2 screen and when i recieved the screen i only open the box to find out it wasnt the screen i needed i needed a samsung s2 4G screen not a 3G and at the time i did not know that they were different, So i contacted the seller and they agreed for me to post the item back and they would refund me. i have sent several messages to this seller and they wouldnt message back untill i said i was going to take this further to ebay and then they messaged me back saying they will put money in my payal that day, it has now been a  week later and still have not recieved any payment in my paypal account and they have not messaged me back again is there anything i can do about this? and if so could you please let me know cheers.