Yeah, there was a "easy" fix by buying the tow truck business and doing a tow truck mission, the thing was that I bought that first and I've done all the tow truck missions before the Taxi purchase, that locked me out of that fix... I had to try other fixes that didn't work as promised, but I end up doing something that did trigger the call. It did take some precious time though...
Basically the same happened me. Sometimes if you lagged out of the online back to single player it fixed it. That's what I done.