I'm so sorry everyone, but I have failed!!
OTA kept referring me to SV, with SV advising me to go back to the OTA. Playing me against each other.
In a last ditched attempt to melt the icy hearts of SV, they categorically blocked me from re-booking onto another carrier. They weren't even nice about it. Kept saying "sorry but this is our policy". Refused accommodation or F&B for the extended delay to my trip. Supervisor was pretty rough with me too - saying that they would never allow it.
I tried to go in a little heavy with threatening legal action for leaving us stranded. Wasn't buying it.
In the end, we booked flights home with Ethiopian Airways - which were a pleasant surprise. I highly recommend them!
I think my next actions are to write to SV and OTA outlining my frustrations. My travel insurance says they will entertain my claim provided I have evidence of the SV drama, so that shouldn't be an issue to get the cost of the ET flights back.
I'm not sure about others experiences with SV, but I don't think I'd book them again even if the price was right. It's not worth the hassle dealing with their call centres.