Using If statement to check cell contents.

Hello, I have two sets of data one in a new spreadsheet with a suffix added and the the second in a master file with both (standard part numbers and some with suffix versions.

I am trying to compare both sets of base data against each other in order to check if the base number exists in the master file. I have a variable value named "FindString" to represent the new data in one workbook, against a variable cell position in the Master file Workbook in Excel. I have declared the "Findstring" as a string from the New file, where the ActiveCell.Formula is looking through the Master file.
This is the formula I am using in VBA to check both files;

'If ((ActiveCell.FormulaR1C1 = "=LEFT(RC1,11)") = FindString) _
Then

Although when both of these cells match contents I am not recieving a "True" response from this logical test.

Can you help?
I am new to VBA and learning as I go.