The computer system our company is using has been changed, and so the invoices are not being issued as scheduled.
Because of this, we have been receiving complaints from our customers constantly.
ご質問ありがとうございます。
"The computer system our company is using has been changed,"＝「わが社のコンピューターシステムが変更されました」
"and so the invoices are not being issued as scheduled. "＝「そしてそれによって、請求書が予定通りに発行されていません。」
"Because of this, we have been receiving complaints from our customers constantly."＝「これにより、お客様から常に苦情を頂いています。」
ご参考に。
アメリカ合衆国 
