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There's no means for us to retrieve the actual message.
You can check your mobile usage in My Account to view the numbers you have contacted instead.
Checking Your Mobile Usage
Let us know should you have further queries. Thank you.
If the phone was backed up before the messages were deleted then in theory when you restore the phone from the back up the messages will be there.(Depending on the make, model of phone, Android version)
In saying that you will loose any messages after that "Back Up" point.
Might be a good idea to contact the manufacturer of the phone to further investigate this.
On our end there is no way for TPG to retrieve those messages.