After being throttled I played around and this fixed it for me. Simply reduce the resources (or change them if you're not already using the maximum allowance.
Go to compute -> instances. Select your instance. On the button on the top right hand corner click Actions -> More Actions ->Edit.
Click the small arrow (▶) symbol beside your flex shape and Edit the OCPU's (and possibly RAM also.) If you're already using 4 OCPU's downscale it to 3. If you're using less than 4 upscale (be mindful if you have 4 instances all using 1 OCPU you'll need to upgrade to PAYG to upscale or delete an instance to free up the allowance).
After a mandatory reboot of the instance the network speed should return to normal for the OCPU's (1gbps per OCPU).
I did not try only modifying the memory. This may work but I doubt it as it is OCPU's which affect network throughput allowance.
Hope this helps everyone who has been throttled!!