URGENT- error on COS

Hello,

My visa expires at the end of January; my employer assigned me a COS to extend my visa however accidentally inputted the wrong salary. The business help desk told them to assign a new COS and we have had to apply to for one (unrestricted) however we think due to urgency we need to use the priority service. Have been unable to get through on the phone to the number we were told to call (0141 555 6027) and due to Christmas rapidly approaching I am worried we won’t get the new COS in time for me to apply for the extension. I called the UKVI helpline and was told that the salary could just be amended in the Sponsor Note section of the COS (and in the UKVI guidance salary is not listed explicitly as a “significant error” which requires a new COS; so now I have conflicting information.

1/ can we just amend the salary in the “sponsor notes” section? or does it count as a "significant error"? . My employer is prepared to supply me with a letter of explanation to include in my applications

2/ any tips on getting through to the priority service line? we called a combined 200 times today.

I had similar problem with my COS. Then my sponsor informed details in sponsor note and sent an email to homeoffice tier2 service. Home office also replied that mail.
On visa application i included that email conversation and also gave a cover letter about all these. I got the visa with no complications.