It is possible you’re unable to reach support as your 6P is out of warranty but as you purchased directly from the Google Store you should be able to make contact HERE. However, as your two-year mandatory retailer’s warranty period has now expired, you would probably be referred to Huawei. The latter has, however, reportedly been sticking firmly to its own one-year manufacturer’s warranty (two in the case of EU Member States) and although they may replace your battery it will be at your own cost.
WashingtonWill has successfully replaced many 6P batteries that he has purchased from eBay from between £15 and £20 – he claims 100% success rate and advises only to buy from reputable sellers that also supply a toolkit.
The majority of issues is who’ve changed the battery either themselves or via a local repairer, have reported success.