I'll second that, Mpower will cure that problem easily. Literally 10 min's.
I'd do it free of charge, and tell them that each time they look at it, it will
remind them of me.
And i bet that will stick in their minds.
Just remember clients like this are not stupid, rip them off and they will
never come back.
Treat them fair, and they WILL, stay loyal. They stick with trusted trades people.