YES!!! I used to really like these! I remember the jingle as well.Does anyone remember McCain's Pizza Rollers?
They mysteriously disappeared from the shelves as you say. I think it could have been due to the fact that after 3 minutes in the microwave the filling had all the basic properties of napalm! Ever seen that Alan Partridge episode?
"Lynn how long did you put that in for? It's hotter than the sun!"

Similar to that microwave popcorn with the block of toffee that you were meant to melt over the top, that got dangerously hot as well, and I haven't seen that stuff for years.