Buying Travel Insurance Whilst Abroad (UK Citizen)

I'm in a bit of a bind. I'm a UK Citizen in Colombia at the moment and planning to stay for a few more months, with no precise leaving date.

I'm currently insured on one of Virgin Travel Insurance's Backpacker schemes, which I bought in the UK before I left. It runs out at the end of this month.

I contacted them to extend it, and it's possible. But, what do you know, the premium for an extended policy is vastly more than the original price I paid.

All told, the premium will be about £100 per month to extend this policy. It's about double what I paid originally. When providing this quote they told me that 'getting other insurance whilst abroad will be very difficult'. It basically feels a bit like extortion, since I'm in a vulnerable position. If I get hit by a car, it doesn't even bear thinking about how I'd go about paying the medical expenses, or worse.

So, at the end of the day, one option is to just pay this ludicrous premium. But I wanted to know if anyone in the community has any experience with buying new travel insurance from a UK insurer whilst abroad? Are there any particular recommended insurers, or resources to find them? Is £100 per month way too high, as I suspect, or would I likely get a similar quote for opening a brand new policy?

If it makes a difference, I'll be staying in Colombia and going to no other countries until I return to the UK. I think that in itself should lower the premium compared to something like backpacker cover. I don't need any contents cover - just medical cover to mitigate against the bankruptcy scenario in case I get really unlucky.