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It has been a long time since we have sent a mail to you or associated with you to offer our service. We hope you are fine and that your business is doing well. We take this opportunity to thank you for giving us the chance to serve you and your company, which we always consider as an honor. Unfortunately, we could not continue our business relationship for a while.
pls correct
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It has been a long time since we offered you our services. We hope that you and your business are doing well. We take this opportunity to thank you for giving us the chance to serve you and your company, which we always consider an honor.
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rajivme It has been a long time since we have communicated sent a mail to you or associated with you regarding to offer our service. We hope you are fine and that your business is doing well. We take this opportunity to thank you for having given giving us the honor [of being able] chance to serve of you and your company in the past. , which we always consider as an honor. Unfortunately, we must discontinue could not continue our business relationship for a while.
Possibly, " . . . thank you for the honor of serving you in the past . . "

Edit. My hat's off to MrM for making short work of a daunting task!