Problems with getting a Refund

NEH

I bought a telephone online last year and it went back because it became faulty after a month. Last month i still hadnt had confirmation that i had had a refund so i chased it up. The company told me that the refund had come back as fraudulent and said they were looking into it. They then phoned me back to say that the refund had gone through and was confirmed by streamline. I said i would confirm with my bank if this was correct. Now last year i did have some moving between banks due to circumstances, however i have checked with both of them and none of them have evidence of a refund going through. I have the proof from the bank to prove this. I have been trying to get hold of them but have had no luck, when they do get back to me i am sure they will again stand by the fact that streamline have confirmed a refund, can i take this any further just so i know, to get my refund. It is less than £20 so i dont know whether it would be better to write it off.

Any help gratefully received