Green Star Energy

when I left my last home I gave green star energy both my gas and electric readings, thinking I was going to get a final bill within 2 weeks I was wrong. I left my home on the 19th of January this year after telephone call after telephone call and having some irish guy thinking its fine to make a joke of it which I was not impressed. I finally have my final bill on the 11th of April I now have got to phone again to now get my refund and its not if you wait for five mins for them to answer its more like 30 mins. this company needs to sort out it customer service side and also its refund side, what if I owed them lots of money it would have been different?