My internet speed at the device is 50 Mbit/s but Fritzbox is receiving 110Mbit/s

The speed you can use is limited by the tariff you have chosen. If you have only ordered a cheap 50 Mbit/s tariff, you can only use a maximum of 50 Mbit/s. If you want to use 100 Mbit/s, you have to change your tariff at o2 to the more expensive 100 Mbit/s tariff and pay more money accordingly.

Thanks for the answer @blablup!

My plan is the Classic L Flex. I pay 34,99 EUR per month.  + I also pay a 15 EUR “unlimited” surcharge so that my bandwidth is never limited or slowed. 

I should get 100 Mbit/s. 

Today I called O2 and they told me that it is normal to get faster speeds at the Fritzbox and less speed at the device…..

I do not believe that this explains my problem

Hello @braddo and welcome to our o2 community :-)

There are several reasons why the speed the router is synced with the DSLAm is higher than the speed that you measure in a speed test. One of the most common reasons is that at the time the DSL connection was established there was no higher speed available.

We can of course have a look into this and try to change the bandwith profile for your connection, regarding the cost of your contract I also strongly recommend to have a look at our current o2 my Home L (flex) tariffs, as already mentioned by @blablup.

Regards,

Lars