At September 30, 2021, we carried a total debt balance (including accrued interest) of €5,527.0 million, of which €1,404.3 million principal amount is related to the € and USD-denominated Senior Secured Fixed Rate Notes due March 2028 and €3,093.5 million principal amount is owed under our 2020 Amended Senior Credit Facility with maturities ranging from April 2028 through April 2029. Our total debt balance at September 30, 2021 also included a principal amount of €362.9 million related to our vendor financing program, while the remainder primarily represents lease obligations associated with the Interkabel Acquisition and other leases.
At September 30, 2021, we carried €362.9 million of short-term debt related to our vendor financing program, all of which is maturing within less than twelve months. This represented increases of respectively €11.9 million versus December 31, 2020 and €15.3 million versus June 30, 2021, reflecting seasonality in some of our scheduled vendor financing payments and positively impacting our Adjusted Free Cash Flow by the same amounts in both periods. For the full year 2021, we continue to anticipate a broadly stable evolution from December 31, 2020 as embedded in our FY 2021 Adjusted Free Cash Flow outlook. As of end-October 2020, the applicable margin on our future short-dated commitments under the vendor financing program has been reduced by another 15 basis points to 1.95% over EURIBOR floored at 0%. This reduced interest cost comes on top of an equivalent 15 basis points margin reduction in February 2020. Given the aforementioned size of the program, this will have a modest accretive impact on our Adjusted Free Cash Flow in 2021 and beyond.
We didn't transact any refinancings or debt amortizations in the first nine months of the year, while substantially all of our floating interest rate risk and foreign exchange currency risk have been hedged until the maturity of such debt instruments through a series of derivatives, improving the visibility on our future Adjusted Free Cash Flow. Excluding short-term liabilities related to our vendor financing program, we face no debt maturities prior to March 2028 with a weighted average maturity of approximately 6.8 years at September 30, 2021. In addition, we also had full access to €555.0 million of undrawn commitments under our revolving credit facilities at September 30, 2021, with certain availabilities up to September 2026.
For more information on our debt instruments and payment schedule at September 30, 2021, we refer to the Q3 2021 Investor & Analyst Toolkit.