Network issue since 3 merger with Vodaphone

I'm on the Isle of Wight (PO33) and have been with Smarty for over a year using an unlimited SIM only card, router and external antenna for my domestic wifi. No problems and good 4G download speeds of >40Mbps - until the merger and tower sharing with Vodaphone customers. Every evening my signal has been well down, tonight it was 3Mbps and obviously no good for streaming.  At first I thought it was my router/antenna but working with the manufacturer I believe the devices are fine and the problem is network congestion.  Anyone else in my area having similar issues?