I grow about 15 species of bamboo, and hopefully this information is useful to @Blackcats7.
The previous ID of Sasa palmata given above, but this is not that bamboo. I think @Cheeesus alluded to this difference.
The plant in the OP's question Pseudosasa japonica, a different species (and genus), but I am not surprised by it being identified as Sasa palmata. Even the Latin name 'Psuedo-' refers to Pseudosasa being a 'fake Sasa', because of their similarities.
Both Sasa palmata and Pseudosasa japonica have been popular in the UK since at least Victorian times, and both have naturalised in parts of the UK. Both have a similar habit of growth, both grow very well in woodland settings with much more shade than other bamboos.
I think both can be very ornamental, especially if you remove the lower leaves on say 0.8-1m of the stems - this is commonly done in East Asia. It turns it into a much more beautiful and impressive looking specimen.
Other than botanical differences in the flowers (which isn't the question) the major differences are height and proportions.
Sasa palmata typically grows to about 1.5m or less (sometimes taller with adequate moisture and fertility). The leaves are about 3x to 5x wider than Psuedosasa japonica, and usually a bit longer, giving it the common name 'broad leaf bamboo'. Altogether, it makes for a much stouter, much more leafy plant.
Pseudosasa japonica can grow 6m high, but usually not more than 3m in the UK. The leaves are much more narrow than Sasa palmata, but still wider than many other commonly grown bamboo (like most Fargesia or Phyllostachys species).
Both bamboo are known as runners. Their rhizome sends out branching, spreading roots away from the centre of the plant, where it sends out new shoots, colonising an area. Hence, both plants can be invasive (explaining how it appeared from below your fence).
You could dig it out, but be aware it will grown back from underneath your fence. This can get exhausting to keep doing the same thing (if it next to lawn, provided you mow when the shoots are short and fresh (and very, very soft), it can be mown down and controlled this way, but if you've too late, the shoots will have shot up and become too woody to control this way). If however you like the plant, you can look after it and prune it to look good, but focus on stopping it spreading further. This can be done by creating a barrier at the soil level, which blocks the rhizome and roots spreading further. This might be done via paving next to it, or a root barrier (search bamboo root barrier) can be dug in, which consists of a rigid but flexible underground fence that gets buried in the ground. It's hard work digging a short trench, but it's perfectly doable without hiring anyone.
Root barriers are really common in landscape gardening, because bamboo are very beautiful, and have a grace and exoticism that few plants have. Both these species are also popular as they provide a quick growing fence and provide a wind break, that grows to a specific height without cutting. l know the RHS have articles related to these root barriers.