I was really disappointed with the quality of their service.
Their attitude towards customers was really disappointing.
こんにちは。
ご質問ありがとうございます。
そんな態度はショックになりますよね。
「接客態度にガッカリした」というのは英語で I was really disappointed with the quality of their service と言ってもいいと思います。
To be disappointed - ガッカリする
Quality - 品格
Service - 接客態度
他の言い方で言うと
Their attitude towards customers was really disappointing. - お客様に対しての態度は本当にガッカリするものでした。
Attitude - 態度
Towards - に対して
Customer - お客様
ご質問のシチュエーションを説明するとこんな感じになります:
They had a lot of staff there, but none of them payed attention to me, even when I raised my hand or called a waitress, the way they were serving drinks was also rude. Their general attitude towards customers was really disappointing.
To pay attention - 気付く
役に立つと幸いです。
よろしくお願いします。
The staff were unprofessional and service was disappointing.
The restaurant had horrible service and horrible staff.
質問ありがとうございます。
こうも言えますよ、
❶ I was really disappointed with the service.
(接客態度にとてもガッカリしました)。
❷ The staff were unprofessional and service was disappointing.
(スタッフはプロ意識に欠けていて、接客態度にもガッカリ)。
❸ The restaurant had horrible service and horrible staff.
(このレストランの接客態度もスタッフも最悪だった)。
こう言えますよ、
The place was full of staff but no one paid attention to us.
(お店はスタッフいっぱいだったけど、誰も私たちに気づきませんでした)。
Their attitude was far from professional ,especially when handling our drinks.
(態度はプロ意識に欠けていて、特に飲み物を扱う時)。
The service was very disappointing.
(接客態度はとても残念だったよ)。
参考になれば嬉しいです！
ロシア連邦 
アメリカ合衆国 
