Read this in a hardcover or paperback anthology book in the public or university libraries back pre-1990.
The story is a human recounting how highly advanced aliens visited Earth and offered all sorts of wonderful miracles of technology and medicine, but the price of their miracle machinery was to strip Earth of all of its natural radioactive elements. Earth paid and the aliens left with their bounty, but as time passed after their departure their miracle machines began to break down. On close examination of the inner workings their machines were found to be powered by the same sorts of radioactive elements they had cleaned Earth out of, and humanity realized it had been ripped off.
The twist at the end came with the narrator talking about the aliens apparently not being knowledgeable in the creation of artificial radioactives, and it turns out the story is being told by a crewman on an Earth ship which has used the aliens' technology and artificially-created radioactives to track them back to their world. At the end of the story he exhorts the reader along the lines of, "Now get out there and tell the bastards that the bill is due." or something strongly to that effect.