How long for a repair...

Happy New Year All 
Purchased a tablet from a third party via *online retailer very big. It had a problem with the battery losing power. Sent it back 10 weeks ago and still no sign of it being returned.
Have informed online retailer 4 times over the last month and they just email them a basic, can we have an update, the company then replies the exact same thing, we will pass this to the repair centre. The item had to be returned to belgium if that makes a difference.
Any ideas on what I should do here, I'm a bit stuck.
Thanks

Purchased a tablet from a third party via *online retailer very big. It had a problem with the battery losing power. Sent it back 10 weeks ago and still no sign of it being returned.
Have informed online retailer 4 times over the last month and they just email them a basic, can we have an update, the company then replies the exact same thing, we will pass this to the repair centre. The item had to be returned to belgium if that makes a difference.
Any ideas on what I should do here, I'm a bit stuck.
Thanks