Debris disks can be seen as the left-overs of giant planet formation and the possible nurseries of rocky planets. While M-type stars out-number more massive stars we know very little about the time evolution of their circumstellar disks at ages older than ∼ 10 Myr. Sub-millimeter observations are best to provide first order estimates of the available mass reservoir and thus better constrain the evolution of such disks. Here, we present ALMA Cycle 3 Band 7 observations of the debris disk around the M2 star TWA7, which had been postulated to harbor two spatially separated dust belts, based on unresolved far-infrared and sub-millimeter data. We show that most of the emission at wavelengths longer than ∼ 300 μm is in fact arising from a contaminant source, most likely a sub-mm galaxy, located at about 6.6ʹʹ East of TWA 7 (in 2016). Fortunately, the high resolution of our ALMA data allows us to disentangle the contaminant emission from that of the disc and report a significant detection of the disk in the sub-millimeter for the first time with a flux density of 2.1±0.4 mJy at 870 μm. With this detection, we show that the SED can be reproduced with a single dust belt.