Ugh it's torture isn't it, having a song stuck that you actively dislike? I get it a lot, but thankfully never usually as badly as I got it during one bad spell, a few years ago.
My head would start playing "I'm walking on sunshine, woah-ohh, I'm walking on sunshine, woah-ohh, I'm walking on sunshine, woah-ohh", and rather than it then resolving to "And don't it feel good!" it would just KEEP ON WALKING ON SUNSHINING INSTEAD, with increasing tempo, settling at around double speed.
For hours at a time, nonstop, every day, sometimes all day. Four words and an exclamation, on endless musical repeat.
The tiniest thing (like seeing some sunshine, or thinking about walking) could set it off. It was so "loud" in my head I couldn't sleep. Sometimes I got so frustrated I'd yell and cry out and hit my pillow. At a fun singing group I attended, I begged them to remove that song from the pieces in rotation, in an attempt to remove at least one trigger. (To their credit, they did.)
This went on for several weeks.
If it wasn't for the fact that the intensity of that earworm was actually a bipolar mania symptom, I'd say that Katrina and the Waves themselves drove me to the edge of sanity, then sang me off the cliff. If I hated that song before, what I feel for it now cannot be described in human words.