Salary sacrifice repayments.

62toffee

Please help! I have scoured the MSE Forum for an answer to a specific (but simple) answer to my question without any luck.

The background to my query is;

• I am employed, with my pension contributions (and my employer's percentage) being paid via salary sacrifice before any deductions from my gross pay. 
• I had a long-term injury and had to claim Employment Service Allowance from the DWP for a period, just before returning to work. 
• Due to a date crossover, my wages were paid in full while receiving my first ESA payments. As a result, the error meant I had a sum to repay to my employer.
• The total overpayment sum was considerably more than my weekly wage and I requested that the sum owed to be repaid in instalments.
• My employer opted to deduct the ESA repayments before any salary sacrifice was processed and a very small amount of wage remained each week.
• Consequently, the company HR decision to implement ESA deductions caused a large shortfall on the amount of employee & employer pension payments.
• I requested the shortfall was to be reimbursed by the company, as they should not have made any deductions before the agreed pension salary sacrifice.
  
• After almost a year, they have yet to answer whether they should or shouldn't have made these deductions before salary sacrifice was implemented.

My question being; Where they right to deduct ESA repayments before implementing the agreed salary sacrifice or should it have been after? 

Thanks in advance.