You can get a full round trip in Business on Iberia or BA for £2720 on these dates for VVI-LHR return. And things like VVI-OPO in Business for £2431
Otherwise I see this, which is near to your original fare, which suggests it is not just an end-on-end fare since it is through routed. I would see if BA can book this, otherwise a competent travel agent should.
Fare 1: Carrier BA TNLN5B SRZ to LON (
rules)Passenger type ADT, round trip fare, booking code H, TCovers VVI-MIA (Economy), MIA-LHR (Premium economy) £425.69
Fare 2: Carrier IB TNNN5O LON to SRZ (
rules)Passenger type ADT, round trip fare, booking code T, HCovers LHR-MIA (Premium economy), MIA-VVI (Economy) £583.41
Bolivia Sales Tax (BO)£150.80BA YQ surcharge (YQ)£299.00US September 11th Security Fee (AY)£8.80United States Immigration User Fee (XY)£11.00United States Customs User Fee (YC)£8.80United States APHIS Passenger Fee Passengers (XA)£6.20Bolivia Exit Tax (YW)£38.10Bolivia Passenger Service Charge (A7)£19.60United Kingdom Passenger Service Charge Departures (UB)£44.91United Kingdom Air Passenger Duty APD (GB)£156.00US Passenger Facility Charge (XF)£3.50Subtotal per passenger£1,755.71Number of passengersx1Subtotal For 1 adult£1,755.71