Upset my boyfriend


I was joking around with my boyfriend and said that he doesn’t last long and it really upset him, I immediately regretted it and said I was sorry however he hung up on me and didn’t talk to me for a day.. can anyone give me advice on what I can say that will make him feel better? I honestly don’t care about how long he lasts it was a joke that was taken to seriously. :(

I’ve apologised a lot already but he’s still upset - pls help.